Semiconductor device with non-volatile memory and random access memory

ABSTRACT

A semiconductor device including a large capacity non-volatile memory and at least one random access memory, said the access time of said device being matched to the access time of each random access memory. The semiconductor memory device is comprised of: a non-volatile memory FLASH having a first reading time; a random access memory DRAM having a second reading time which is more than 100 times shorter than the first reading time; a circuit that includes a control circuit connected to both the FLASH and the DRAM and enabled to control accesses to those FLASH and DRAM; and a plurality of I/O terminals connected to the circuit. As a result, FLASH data is transferred to the DRAM before the DRAM is accessed, thereby matching the access time between the FLASH and the DRAM. Data is written back from the DRAM to the FLASH as needed, thereby keeping data matched between the FLASH and the DRAM and storing the data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. application Ser.No. 11/152,526 filed Jun. 13, 2005, which is a Continuation applicationof U.S. application Ser. No. 10/861,452 filed Jun. 7, 2004, which is aContinuation application of U.S. application Ser. No. 10/164,905 filedJun. 10, 2002. Priority is claimed based on U.S. application Ser. No.11/152,526 filed Jun. 13, 2005, which claims the priority U.S.application Ser. No. 10/861,452 filed Jun. 7, 2004, which claims thepriority U.S. application Ser. No. 10/164,905 filed Jun. 10, 2002, whichclaims the priority date of Japanese Patent Application No. 2001-174978filed Jun. 11, 2001, all of which is incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stacked memory semiconductor devicethat includes various kinds of memories, and, more particularly, thepresent invention relates to a combination of said stacked memories, amethod for controlling those memories, and a structure for integratingthose memories into a multi-chip module.

2. Description of the Background

The following documents are referenced in this specification. Thedocuments are numbered, and hereinafter, they will be described withreference to these numbers. [“Document 1”]: LRS1337 Stacked Chip 32MFlash Memory and 4M SRAM Data Sheet (Apr. 21, 2000); [“Document 2”]:Official Gazette of JP-A 299616/1991 (Official Gazette of EuropeanPatent No. 566,360, Oct. 20, 1993); [“Document 3”]: Official Gazette ofJP-A 146820/1993; and [“Document 4”]: Official Gazette of JP-A5723/2001.

Document 1 discloses a stacked semiconductor memory in which a flashmemory (capacity: 32M bits) and an SRAM (capacity: 4M bits) are moldedtogether on a stacked chip in an FBGA package. The flash memory and theSRAM share address input terminals and data I/O terminals connected tothe input/output electrodes of the FBGA package respectively. However,the control terminals of the memories are independent of each other.

FIG. 17 in Document 2 shows a stacked semiconductor memory in which aflash memory chip and a DRAM chip are molded together in a lead framepackage. FIG. 1 in Document 2 shows a stacked memory in which a flashmemory and a DRAM share address input terminals, data I/O terminals, aswell as a control terminal connected to the input/output electrodes ofthe package respectively.

FIG. 1 in Document 3 shows a system comprised of a flash memory used asa main storage, a cache memory, a controller, and a CPU.

FIG. 2 in Document 4 shows a semiconductor memory comprised of a flashmemory, a DRAM, and a transfer control circuit.

An examination of cellular telephones, as well as memory modules usedfor those cellular phones, confirms that, in each of those memorymodules, a flash memory and an SRAM are mounted together in one package.Cellular phones are often provided with various functions (related tothe distribution of music, games, etc.), and the size of thecorresponding application programs, data, and work areas thereof areever increasing. It is to be expected that cellular phones with largercapacity flash memories and SRAMs will soon be needed. Additionally, therecent enhancement of cellular phone functionalities may also requirelarger capacity memories.

Presently, a cellular phone uses a flash memory that employs so-called“NOR memory cell arrays.” The NOR flash memory employs memory cellarrays that suppress the parasitic resistance. The NOR flash memorylowers the resistance by providing one through-hole to bit line for twocells connected in parallel. This reduces the reading time to about 80ns, which is almost equal to the reading time of a large capacity,medium access speed SRAM. On the contrary, because one through-hole tobit line must be provided for two cells, the ratio of the through-holeto bit line area to the chip area increases such that the one-bit memorycell area also increases. It has been difficult to give a large capacityto the NOR flash memory. This has been a problem.

Typical large capacity flash memories are roughly classified into twotypes: AND flash memories that employ the AND memory arrays and NANDflash memories that employ the NAND memory arrays. In each of theseflash memories, one through-hole to bit line is formed for 16 to 128cells, so that the flash memory can form high density memory arrays.Consequently, it is possible to reduce the one-bit area per memory cellmore than that of NOR flash memories. A larger capacity can thus begiven to those flash memories. On the contrary, the reading time foroutputting the first data becomes about 25 μs to 50 μs, so that thoseflash memories can not easily match the read access speed of an SRAM.

A flash memory can keep data even when the power supply to the cellularphone (or other device) is shut off. However, power is kept supplied toan SRAM so as to hold data therein even when the power to the cellularphone is off. To hold data in an SRAM for an extended period of time,therefore, the data retention current should be minimized. Largecapacity SRAMs are confronted with problems in that the data retentioncurrent increases in proportion to an increase in the capacity of thememory and the data retention current increases due to an increase inthe gate leakage current. This occurs because a tunnel current flows tothe substrate from a gate when the oxide insulator of the MOS transistoris thinned in a micro-machining process meant to increase the capacityof the SRAM. As a result, the data retention current increases. It hasbeen noted that it is increasingly difficult to reduce the dataretention current in larger capacity SRAMs.

To address the above-mentioned problems, the present inventionpreferably provides a ROM that has an increased memory capacity and theability to read and write data quickly, as well as a RAM that has anincreased memory capacity and requires reduced data retention current.

SUMMARY OF THE INVENTION

In at least one preferred embodiment, the present invention provides asemiconductor device comprising: a non-volatile memory having a firstreading time; a random access memory RAM having a second reading time,which is more than 100 times shorter than the first reading time; acircuit that includes a control circuit that is connected to andcontrols access to both the non-volatile memory and the random accessmemory; and a plurality of input/output terminals connected to thecircuit.

The control circuit is preferably adapted such that at least part of thedata stored in the non-volatile memory (flash memory) is transferred tothe DRAM (random access memory) before operation of the device. To writedata in the non-volatile memory, the data should be initially written tothe RAM and then written to the non-volatile memory from the RAM betweenaccess requests from devices located outside the semiconductor device.In addition, the control circuit may be adapted to control such thatrefreshment of the DRAM is hidden from external when the RAM is a DRAM.

BRIEF DESCRIPTION OF THE DRAWINGS

For the present invention to be clearly understood and readilypracticed, the present invention will be described in conjunction withthe following figures, wherein like reference characters designate thesame or similar elements, which figures are incorporated into andconstitute a part of the specification, wherein:

FIG. 1 is a block diagram of a memory module of the present invention;

FIG. 2 is a block diagram of the chip 2 shown in FIG. 1;

FIG. 3 is an example of address maps of the memory module of the presentinvention;

FIG. 4 is an example of the address maps of the memory module of thepresent invention;

FIG. 5 is an example of the operation of the memory module of thepresent invention, executed when the module is powered;

FIG. 6 is a flowchart of data transfer from a FLASH to a DRAM in thememory module of the present invention;

FIG. 7 is a flowchart of data transfer from the DRAM to the FLASH in thememory module of the present invention;

FIGS. 8A and 8B are flowcharts of reading/writing from/to the DRAM inthe memory module of the present invention;

FIG. 9 is an example of the operation of a data renewing managementcircuit CPB shown in FIG. 2;

FIG. 10 is a flowchart of the operation of the memory module of thepresent invention, executed when the power supply to the module is shutoff;

FIG. 11 is an example of the operation of the DRAM executed with a LOADcommand issued from external;

FIG. 12 is an example of the operation of the DRAM executed with a STOREcommand issued from external;

FIGS. 13A and 13B show an example of reading/writing data from/to theDRAM in the memory module of the present invention;

FIG. 14 is an example of reading data from the DRAM when a read requestis issued from external to the DRAM while data is read from the DRAMwith a STORE command;

FIG. 15 is a block diagram of the FLASH shown in FIG. 1;

FIG. 16 is a timing chart of reading data from the FLASH shown in FIG.15;

FIG. 17 is another block diagram of the memory module of the presentinvention;

FIG. 18 is a block diagram of the FLASH shown in FIG. 17;

FIG. 19 is a timing chart for reading data from the FLASH shown in FIG.18;

FIG. 20 is a block diagram of the DRAM;

FIG. 21 is another block diagram of the memory module of the presentinvention;

FIG. 22 is a block diagram of the chip 2 shown in FIG. 21;

FIG. 23 is an example of address maps of the memory module of thepresent invention;

FIG. 24 is an example of the memory maps of the memory module of thepresent invention;

FIG. 25 is an example of the operation of the memory module of thepresent invention, executed when the module is powered,

FIG. 26 is an example of the operation of the memory module of thepresent invention, executed when the module is powered;

FIGS. 27A to 27C show an example of the access priority order for theoperation of the memory module of the present invention;

FIGS. 28A and 28B show an example of the operation of the DRAM, executedwith LOAD and STORE commands issued from external;

FIGS. 29A and 29B show an example of the operation of the DRAM, executedin response to an access from external while the DRAM is accessed withLOAD and STORE commands;

FIG. 30 is a timing chart for the memory module of the presentinvention;

FIG. 31 is a timing chart for the memory module of the presentinvention;

FIG. 32 is a block diagram of an SRAM;

FIGS. 33A and 33B show an example of mounting chips on the memory moduleof the present invention;

FIGS. 34A and 34B show an example of mounting chips on the memory moduleof the present invention;

FIG. 35 is another block diagram of the memory module of the presentinvention;

FIG. 36 is a block diagram of the chip 2 shown in FIG. 35.

FIG. 37 is an example of memory maps of the memory module of the presentinvention;

FIGS. 38A to 38C are flowcharts describing a process by which the DRAMis accessed and refreshed concurrently from external;

FIGS. 39A to 39C are flowcharts describing a process by which the DRAMis accessed from external and in the memory module of the presentinvention concurrently;

FIGS. 40A and 40B show exemplary DRAM refreshing methods;

FIGS. 41A and 41B are charts which describe a process by which an accessis taken over when WORK and REF. periods are changed over;

FIG. 42 is a timing chart of the memory module of the present invention;

FIGS. 43A and 43B show an example of mounting chips on the memory moduleof the present invention;

FIGS. 44A and 44B show an example of mounting chips on the memory moduleof the present invention; and

FIG. 45 is a block diagram of a cellular phone including the memorymodule of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the figures and descriptions of the presentinvention have been simplified to illustrate elements that are relevantfor a clear understanding of the present invention, while eliminating,for purposes of clarity, other elements that may be well known. Those ofordinary skill in the art will recognize that other elements aredesirable and/or required in order to implement the present invention.However, because such elements are well known in the art, and becausethey do not facilitate a better understanding of the present invention,a discussion of such elements is not provided herein. The detaileddescription will be provided hereinbelow with reference to the attacheddrawings.

Hereunder, the preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.Although the circuit elements of each block in each of the embodimentsare not specifically limited, the elements are assumed to be formed on asemiconductor substrate such as single crystal silicon using knownintegrated circuit techniques, such as CMOS (complementary MOStransistor) and the like.

First Exemplary Embodiment

FIG. 1 shows a first embodiment of a memory module, which is an exampleof the semiconductor device of the present invention. This memory moduleis preferably comprised of three chips. Each of those three chips is nowdescribed.

The chip 1 (FLASH) is a non-volatile memory. This non-volatile memorymay be a ROM (Read Only Memory), an EEPROM (Electrically Erasable andProgrammable ROM), a flash memory, or any similar storage element. Atypical example of the non-volatile memory used as chip 1 in thisembodiment is a NAND flash memory (to be described below) in the broadsense. The NAND flash memory may have a memory capacity of about 256 Mband a reading time (time required between a read request and dataoutput) of about 25 μs to 50 μs, which is comparatively slow. On thecontrary, the SDRAM used as chip 3 has a large memory capacity of about256 Mb and a reading time of about 35 ns. Specifically, the reading timeof chip 3 is preferably more than 100 times shorter than that of thechip 1. This provides an excellent contrast with the NOR flash memorywhose reading time is about 80 ns, which is on the same order ofmagnitude of the reading time of the DRAM. The present inventionprovides a solution to efficient accesses to memories, like these, withreading times that differ significantly from each other.

The DRAM is preferably divided into various kinds such as EDO, SDRAM,DDR-SDRAM, and similar types according to differences in the internalconfiguration and the interface type among them. Although any DRAM maybe used as this memory module, this exemplary embodiment employs theSDRAM, which is a typical DRAM synchronized with a clock. Chip 2(CTL_LOGIC) is provided with a control circuit for controlling chips 1and 3.

The present memory module receives addresses (A0 to A15), a clock signal(CLK), and command signals (CKE, /CS, /RAS, /CAS, /WE, DQMU/DQML) inputfrom external. It should be noted here that the terms “external” and“from external” refer to devices/operations outside of the memory moduleof the present invention. The memory module is powered via S-VCC, S-VSS,L-VCC, L-VSS, F-VCC, F-VSS, D1-VCC, and D1-VSS. The memory module usesDQ0 to DQ15 for data input/output. The memory module uses a so-calledSDRAM interface for operations.

Chip 2 supplies signals required to operate chips 1 and 3. Chip 2supplies a serial clock (F-SC), addresses (A0 to A15), flash data (I/O0to I/O7), and commands (F-CE, F-/OE, F-/WE, F-SC, F-/RES, F-CDE,F-RDY/BUSY) to chip 1. In addition, chip 2 supplies a clock (D1-CLK),addresses (D1-A0 to D1-A14), commands (D1-CKE, D1-/CS, D1-/RAS, D1-/CAS,D1-/WE, D1-DQMU/DQML), and DRAM data (D1-DQ0 to D1-DQ15) to chip 3.

Hereunder, each command signal will be described briefly. The signalsinput to chip 2 are as follows: the CLK is a clock signal; the CKE is aclock enable signal; the /CE is a chip select signal; the /RAS is a rowaddress strobe signal; the /CAS is a column address strobe signal; the/WE is a write enable signal; and the DQMU/DQML is an I/O data masksignal. The signals input to chip 3 are as follows: the D1-CLK is aclock signal; the D1-CKE is a clock enable signal; the D1-/CS is a chipselect signal; the D1-/RAS is a row address strobe signal; the D1-/CASis a column address strobe signal; the D1-/WE is a write enable signal;and the D1-DQMU/DQML is an I/O data mask signal. The signals input tochip 1 are as follows: the F-/CE is a chip enable signal; the F-/OE isan output enable signal; the F-/WE is a write enable signal; the F-SC isa serial clock signal; the F-/RES is a reset signal; the F-CDE is acommand data enable signal; the F-RDY/BUSY is ready/busy signal; and theI/O0 to I/O7 are I/O signals used to input addresses, as well asinput/output data.

The control circuit (CTL_LOGIC) of chip 2 selects a command registerprovided in the control circuit (CTL_LOGIC) of chip 2, the DRAM of chip3, or the FLASH of chip 1 according to an address value received fromexternal. Accesses from external can be distinguished among access tothe command register, access to the DRAM, and access to the FLASHaccording to a value preset in the control register provided in thecontrol circuit (CTL_LOGIC). An SDRAM interface is preferably used toreceive each of these accesses.

The DRAM is divided into a work area and a FLASH data copy area. Thework area is used as a work memory in which programs are executed, andthe FLASH data copy area is used as a memory for enabling FLASH data tobe copied therein.

The command register in the control circuit (CTL_LOGIC) is accessed towrite a LOAD instruction code and a STORE instruction code, therebycopying (loading) FLASH data into the FLASH data copy area and writingback (storing) data into the FLASH from the FLASH data copy area of theDRAM.

In a case in which an address for accessing the command register isinput via address signal lines (A0 to A15), a WRITE command is input viaa command signal line (CKE, /CS, /RAS, /CAS, /WE, DQMU/DQML), and a LOADinstruction code followed by the start and end addresses of an addressrange for selecting the FLASH are input to the command register via theI/O data signal lines (D1-DQ0 to D1-DQ15). The LOAD instruction code, aswell as the start and end addresses with respect to the loading arewritten to the command register. After this process, the target data isread from the address range between the start and end addresses in theflash memory and is then transferred to the FLASH data copy area of theDRAM. Consequently, the FLASH data is held in the DRAM.

When a STORE instruction code, as well as start and end addresses forselecting the FLASH are written in the command register, the target datais written in the address range between the start and end addresses fromthe FLASH data copy area of the DRAM.

A value may be preset in the control register provided in the controlcircuit (CTL_LOGIC) to determine address correspondence between anaddress range in the FLASH and an address range in the FLASH data copyarea of the DRAM.

The reliability of the FLASH is degraded when rewriting therein isrepeated, whereby written data is read incorrectly and rewriting issometimes disabled. When the control circuit (CTL_LOGIC) reads data fromthe FLASH, chip 2 (CTL_LOGIC) preferably checks whether or not read datacontains an error, corrects the error if any, and transfers thecorrected data to the DRAM.

When the control circuit (CTL_LOGIC) writes data to the FLASH, chip 2(CTL_LOGIC) checks whether or not the writing is performed successfully.When chip 2 detects an error (not successful in an address), chip 2writes the data to another address. This checking operation is so-called“replacement processing.” Chip 2 also manages such a fail address andthe replacement processing executed for the fail address.

When accessing the FLASH data copy area of the DRAM, addresses forselecting the FLASH and a READ command are input via address signallines (A0 to A15) and a command signal line (CKE, /CS, /RAS, /CAS, /WE,DQMU/DQML). The control circuit of chip 2 then accesses the DRAM to readthe target data from the address range in the FLASH data copy area ofthe corresponding DRAM. Consequently, data may be read from the FLASHdata copy area of the DRAM at the same speed as that of the DRAM.

To access the work area in the DRAM, address and command signalsrequired for the access are input to the command register. The controlcircuit (CTL_LOGIC) then generates an address for the work area in theDRAM and accesses the DRAM. For a read access, the data read from theDRAM is output to the data I/O lines (DQ0 to DQ15) via the DRAM data I/Olines (D1-DQ0 to D1-DQ15). For a write access, write data is input viadata I/O lines (DQ0 to DQ15) of the memory module, then input to theDRAM via DRAM data I/O lines (D1-DQ0 to D1-DQ15).

As described above, the memory module of the present invention that usesthe SDRAM interface makes it possible to read data from the FLASH almostat the same speed as that of the DRAM because the module includes anarea enabled to copy part or all of the data from the FLASH and transferthe data into the DRAM before operation of the module. Data may also bewritten to the FLASH at the same speed as that of the DRAM because thedata is initially written to the DRAM and thereafter written back to theFLASH as needed. To read data from the FLASH in the memory module, theprocessing can be sped up and the reliability can be assured becauseerrors are detected and corrected and replacement processing isundertaken for each fail address in which data is not correctly written.Additionally, because a large capacity DRAM is preferably used for thememory module, a FLASH data copy area as well as a large capacity workarea may be secured in the DRAM, allowing the memory module to cope withthe enhanced functions of any cellular telephone.

FIG. 2 shows a block diagram of chip 2 (CTL_LOGIC). Chip 2 (CTL_LOGIC)is a control circuit that receives signals from external via an SDRAMinterface to control both chip 3 (DRAM) and chip 1 (FLASH). Theoperation of each circuit block of chip 2 (CTL_LOGIC) will now bedescribed.

The initialization circuit INT initializes the control register in amemory management unit MMU and the DRAM when the DRAM is powered. Thememory management unit MMU translates addresses input from externalaccording to a value preset in a built-in control register to select atarget to access, that is, a command register REG, a DRAM work area, aFLASH data copy area, or the FLASH. The value in the control register isinitialized by the initialization circuit INT when the DRAM is powered.Afterwords, the value may be updated when an MMU CHANGE command is inputto the command register REG. When data is written in an address of theFLASH data copy area of the DRAM, a data renewing address managementcircuit CPB holds the address information. The command register REGholds LOAD, STORE, MMU CHANGE and other instruction codes, as well asthe start and end addresses for loading, storing, and other functions.

A data buffer R/W BUFFER holds data read/written from/to the DRAM, aswell as data temporarily read/written from/to the FLASH. A clock bufferCLKBUF supplies a clock signal to both the DRAM and the FLASH controlcircuit FGEN. A command generator COM_GEN generates commands requiredfor accesses to the DRAM. An access controller A_CONT generatesaddresses for controlling all of chip 2 and accessing the DRAM. A powermodule PM supplies power to the DRAM and controls the power supply. AFLASH control signal generator FGEN controls reading/writing datafrom/to the FLASH.

An error correction circuit ECC checks whether or not the data read fromthe FLASH contains any error and corrects the error when detected. Areplacement processing circuit REP checks whether or not writing to theFLASH is done correctly. When writing to an address fails, the REPwrites the data to another address previously prepared in the FLASH(i.e., address replacement processing).

The operation of the above-described memory module will now bedescribed. The initialization circuit INT initializes the controlregister located in the memory management unit MMU and the DRAM when theDRAM is powered. In the case where the command register REG is selectedand a LOAD command is written in the command register REG, data transferfrom the FLASH to the DRAM begins. At first, the FLASH control signalgenerator FGEN reads target data from the FLASH. When no error isdetected in the data read from the FLASH, the data is transferreddirectly to the data buffer R/W BUFFER. When an error is detected in thedata, the error correction circuit ECC corrects the error and transfersthe corrected data to the data buffer R/W BUFFER. After this, the DRAMreceives a WRITE command from the command generator COM_GEN, addresssignals from the access controller A_CONT, and data read from the FLASHfrom the data buffer R/W BUFFER. The data is then written to the FLASHdata copy area of the DRAM.

When data is written to the FLASH data copy area of the DRAM, the datarenewing management circuit CPB holds the write address information.When the command register REG is selected and a STORE command is writtento the command register REG, data transfer from the FLASH data copy areaof the DRAM to the FLASH begins.

Initially, the DRAM receives a READ command from the command generatorCOM_GEN and address signals from the access controller A_CONT wherebythe target data is read from the DRAM. The data read from the DRAM istransferred to the FLASH controller FGEN via the data buffer R/W BUFFER,then the FLASH control signal generator FGEN writes the data in theFLASH.

The address replacement processing circuit REP checks whether or notwriting is done successfully and terminates the processing when thewriting is done successfully. When the writing in an address fails, datais written in another address prepared beforehand in the FLASH (addressreplacement processing). When such a replacement processing is done, thecircuit REP holds and manages the address information that denotes sucha fail address in which the replacement processing is done. The datarenewing management circuit CPB clears the information of each FLASHaddress in which writing is ended sequentially from DRAM addressinformation held therein. In this way, the data renewing managementcircuit CPB can manage the latest one of the addresses in which data isupdated.

When the DRAM work area and the FLASH data copy area are selected and aREAD command is received by the memory module, the DRAM receives theREAD command signal from the command generator COM_GEN and addresssignals from the access controller A_CONT whereby the target data isread from the DRAM. When the DRAM work area and the FLASH data copy areaare selected and a WRITE command is received by the memory module, theDRAM receives the WRITE command signal from the command generatorCOM_GEN, address signals from the address generator A_CONT, and datafrom the data buffer R/W BUFFER whereby the target data is written inthe DRAM.

The data renewing management circuit CPB, when receiving a DRAMPOWER-OFF command via the signal PS line, transfers the DRAM datacorresponding to the address held therein to the FLASH. Initially, theDRAM receives a READ command and address signals from the commandgenerator COM_GEN and the access controller A_CONT, respectively,whereby target data is read from the DRAM. The data read from the DRAMis transferred to the FLASH controller FGEN via the data buffer R/WBUFFER and is then written in the FLASH by the FLASH control signalgenerator FGEN.

The data renewing management circuit CPB then clears information of eachFLASH address in which data is already written sequentially from theDRAM address information held therein. When all the data items arewritten to the FLASH corresponding to the held addresses, the addressinformation in the data renewing management circuit CPB is all cleared.After all the data items are transferred from the DRAM to the FLASH, thepower to the DRAM is shut off. This power shut-off reduces the powerconsumption of the DRAM.

To restart the DRAM after the power supply to the DRAM is shut off, theDRAM must be powered again with a POWER-ON command input from the PSsignal line and then initialized by the access controller (A_CONT) in apredetermined initialization procedure as instructed by theinitialization circuit INT.

FIGS. 3 and 4 show memory maps in which addresses are translated by thememory management unit MMU. The user may select any of the memory mapsaccording to a value set in the control register in the MMU. Althoughnot specifically limited, in this embodiment, the memory maps areassumed to be formed for a memory module in which the non-volatilememory includes a recording area of 256+8 Mb and the DRAM includes arecording area of 256 Mb. The capacity of the command register REG is 16kb.

In the maps shown in FIG. 3, the row addresses (A0 to A15) and thecolumn addresses (A0 to A9) input via the address signal lines A0 to A15are translated by the memory management unit MMU to those used in thecommand register REG (8 kb), the DRAM work area (128M bits), the DRAMFLASH copy area (128M bits), and the FLASH (256M bits+8 Mb). Althoughnot specifically limited, the command register REG, the DRAM, and theFLASH are mapped at the bottom of each memory map address space. Thecommand register REG in the chip 2 (CTL_LOGIC) receives instructioncodes such as LOAD, STORE, MMU CHANGE, POWER-OFF, etc., as well as thestart and end addresses for loading, storing, etc. written therein fromexternal.

The DRAM is shown divided into a work area (128M bits) and a FLASH datacopy area (128M bits). The work area is used as a work memory in whichprograms are executed. The FLASH data copy area is used to copy and holdpart of the data stored in the FLASH area. When part of the data is tobe copied from the FLASH to the FLASH data copy area, the memorymanagement unit MMU determines the address correspondence between anaddress range in the FLASH and an address range in the FLASH data copyarea according to a value preset in the control register located in theMMU. FIG. 3 shows an example of such address correspondence denotingthat the data in the A1 area (64 Mb) and the C1 area (64 Mb) in theFLASH area can be copied into the A area (64 Mb) and the C area (64 Mb)in the FLASH copy area of the DRAM. It is also possible to change theaddress correspondence so that the data in the B1 area (64 Mb) and theD1 area (64 Mb) in the FLASH can be copied into the FLASH copy area ofthe DRAM by changing the value preset in the internal control registerlocated in the memory management unit MMU. The value in the MMU controlregister can be changed from external by writing an MMU CHANGE commandand a new register value into the command register.

Although not specifically limited, the FLASH (256 Mb+8 Mb) is showndivided into a main data area MD-Area (A1, A2, B1, B2, C1, C2, D1, D2:255.75 Mb) and a replacement area Rep-Area (E1, E2: 8.25 Mb). The maindata area MD-Area is shown further divided into a data area (A1, B1, C1,D1) and a redundant area (A2, B2, C2, D2). The data area is used tostore programs and data, and the redundant area is used to store ECCparity data and other data required to detect and correct errors. Datain the FLASH data area is transferred to the FLASH copy area of theDRAM, or data in the FLASH copy area of the DRAM is transferred to theFLASH data area.

The reliability of the FLASH is degraded when rewriting is repeatedtherein, whereby data incorrect may be written and rewriting may bedisabled. The replacement area is meant to replace a fail area (failarea B, fail area C) with another area for writing the data therein. Thesize of the replacement area is not specifically limited, but it shouldbe determined so as to assure the reliability of the FLASH.

Data is transferred from the FLASH to the DRAM as follows. To transferdata from the FLASH area A1 to the FLASH copy area A located in theDRAM, a LOAD command as well as start and end addresses SAD and EAD forthe A1 area in the FLASH are written to the command register.Thereafter, the control circuit (CTL_LOGIC) reads the data from theaddress range specified by the start and end addresses FSAD and FEAD ofthe FLASH area A1 and then transfers the data to the address rangespecified by the DSAD and DEAD of the FLASH copy area A in the DRAM. Thememory management unit MMU preferably determines the correspondencebetween the address ranges (FSAD→DSAD and FEAD→.DEAD).

For error correction, when reading data from the FLASH, the controlcircuit reads the data from the FLASH data area A1 and the ECC paritydata from the redundant area A2, respectively. When an error is detectedin the read data, the error correction circuit ECC corrects the errorand then transfers only the corrected data to the DRAM.

Data is transferred from the DRAM to the FLASH as follows. To transferdata from the FLASH copy area A to the FLASH area A1, a STORE command aswell as start and end addresses SAD and EAD for the FLASH area A1 arewritten to the command register. The control circuit (CTL_LOGIC) thenreads the target data from the address range specified by the start andend addresses DSAD and DEAD of the FLASH copy area A located in the DRAMand then writes the data in the address range specified by the FSAD andFEAD of the FLASH area A1. The memory management unit MMU preferablydetermines the correspondence between the address ranges (DSAD FSAD andDEAD FEAD).

For error correction, when writing data to the FLASH, the errorcorrection circuit ECC generates ECC parity data. The data read from theDRAM by the FLASH control circuit FGEN is written to the FLASH data areaA1, and the generated ECC parity data is written to the redundant areaA2. The address replacement processing circuit REP checks whether or notthe writing is performed successfully. If the write is successful, thecircuit REP terminates the processing. If the write fails, the circuitREP selects another address in the FLASH replacement area and writes thedata to the replacement data area E1 and the generated ECC parity datato the redundant area E2, respectively.

A description will now be made of a process for reading data from theFLASH copy area A located in the DRAM. When an address FAD0 of the FLASHA1 area and a READ command are input to the command register fromexternal, the MMU translates the address FAD0 to an address DAD0 of theFLASH copy area A in the corresponding DRAM. Consequently, the DRAM isselected, and FLASH data copied to the DRAM can be read therefrom. Inother words, data in the FLASH can be read at the same speed as that ofthe DRAM.

Data is read from the work area located in the DRAM as follows. When anaddress WAD0 of the work area and a READ command are input to thecommand register from external, the MMU outputs the address WAD0 to theaccess controller A_CONT. Consequently, data can be read from theaddress WAD0 of the work area in the DRAM.

Data is written to the FLASH copy area A in the DRAM as follows. When anaddress FAD0 of the FLASH area A1, a WRITE command, and write data areinput to the command register from external, the MMU translates theaddress FAD0 to an address DAD0 of the FLASH copy area A in thecorresponding DRAM. Consequently, the DRAM is selected, and data iswritten in the FLASH copy area A in the DRAM. When data is written inthe FLASH copy area A in the DRAM corresponding to the FLASH data areaA1 in this way, FLASH data can be written at the same speed as that ofthe SRAM.

Data is written to the DRAM work area as follows. When an address WAD0of the work area, a WRITE command, and input data are input to thecommand register from external, the access controller A_CONT outputs theaddress WAD0 to the DRAM. Consequently, data is written in the addressWAD0 in the DRAM work area.

FIG. 4 shows memory maps when the FLASH data copy area is reserved over192 Mb in the DRAM. The copy area is therefore larger than that shown inFIG. 3. In the maps shown in FIG. 4, the memory management unit MMUtranslates row addresses (A0 to A15) and column addresses (A0 to A9)input via the address signal lines A0 to A15 to addresses used in theregister area, the DRAM work area (64 Mb), the FLASH data copy area inthe DRAM (192 Mb), and the FLASH (256 Mb).

The user may freely select any of the memory maps in the user's systemby changing the preset value in the control register located in the MMU.The preset value in the control register in the MMU may be changed fromexternal by writing an MMU CHANGE instruction code and a new registervalue in the command register.

FIG. 5 shows initialization of the control circuit (CTL_LOGIC) whenpower is supplied. When the DRAM is powered in a time period T1, thecontrol circuit (CTL_LOGIC) is initialized in reset period T2. The valuein the control register provided in the memory management unit MMU isalso initialized in period T2. In period T3, the initialization circuitINT initializes both the DRAM and the FLASH. When the initializationends, the memory module goes into the idle state T4 and prepares toaccept accesses from external.

FIG. 6 shows a flowchart of data transfer from the FLASH to the DRAM.When a LOAD command and addresses for selecting the FLASH are input(step 2) while the memory module waits for a command from external inthe idle state (step 1), the memory module reads the data correspondingto the input FLASH address range and the ECC parity data (step 3). Anerror check is then performed for the read data (step 4). If an error isdetected in the data, the error is corrected (step 5), and the correcteddata is written to the buffer (step 6). If no error is detected, thedata is written directly to the buffer R/W BUFFER (step 6). When data istransferred from the buffer R/W BUFFER to the DRAM, a check is made todetermine whether or not a refresh request is issued to the DRAM (step7). If a refresh request is issued, a refresh processing is done (step8) and data is written to the DRAM (step 9). If no refresh request isissued, data is written to the DRAM immediately (step 9).

FIG. 7 shows a flowchart of data transfer from the DRAM to the FLASH.When a STORE command and addresses for selecting the FLASH are input(step 2) while the memory module waits for a command from external inthe idle state (step 1), the memory module begins reading the targetdata from the address range of the DRAM. At this time, the memory modulechecks whether or not a refresh request is issued to the DRAM (step 3).If a refresh request is issued, the memory module refreshes the DRAM(step 4) and then reads data from the DRAM (step 5). If no refreshrequest is issued, the memory module reads the target data from the DRAMimmediately (step 5). The read data is transferred to the buffer R/WBUFFER (step 6) and is then written into the FLASH (step 7). To writedata in the FLASH (step 7), the memory module writes the data read fromthe DRAM and the ECC parity data generated by the error correctioncircuit ECC into the FLASH, respectively. The memory module then checkswhether or not the writing in the FLASH is successful (step 8). If thewrite is successful, the processing is terminated (step 10). If thewrite fails, the memory module selects another address (step 9) and thenwrites the data in the address (step 7). Thereafter, the memory modulerechecks whether or not the writing is successful (step 11). Whensuccessful, the processing is terminated (step 10).

FIG. 8A shows a flowchart of commands issued from external for readingdata from a DRAM provided in the memory module. FIG. 8B shows aflowchart of commands issued from external for writing data into theDRAM provided in the memory module. Commands are preferably input fromexternal via the SDRAM interface respectively.

The flowchart shown in FIG. 8A will now be described. The memory modulewaits for a command from external in the idle state (step 1). When anACTIVE command and a row address (step 2), and then a READ command and acolumn address are received from external (step 3), the memory modulereads the data from the DRAM memory cells selected by the input row andcolumn addresses and outputs the data to external via the I/O datasignal lines (DQ0 to DQ15). Receiving a PRECHARGE command (step 4), thememory module goes into the idle state.

The flowchart shown in FIG. 8B will now be described. At first, thememory module waits for a command from external in the idle state (step1). When an ACTIVE command and a row address (step 2), and then a WRITEcommand and a column address are received from external (step 3), thememory module writes the data input via the I/O data signal lines (DQ0to DQ15) in the DRAM memory cells selected by the input row and columnaddresses. Receiving a PRECHARGE command (step 4), the memory modulegoes into the idle state.

FIG. 9 shows a flowchart of address holding and address clearing by thedata renewing management circuit CPB. When data is written to the FLASHcopy area in the DRAM in response to a WRITE command received fromexternal (step 1), a flag signal corresponding to the write address iswritten to a flag register provided in the data renewing managementcircuit CPB (step 2). When a STORE command and addresses are input fromexternal, data transfer from the FLASH data copy area in the DRAM to theFLASH begins (step 3). Then, the memory module repeatedly checks whetheror not the transfer is completed (step 4). When the check result is“YES” (completed), the CPB clears the flag in the transfer completeaddress in the flag register.

FIG. 10 shows a flowchart of the operation of the memory module when aDRAM POWER-OFF command is input thereto. When a POWER-OFF command isinput to the command register, all the data in the FLASH data copy areaof the DRAM, which is not written back in the FLASH, is transferred tothe FLASH.

When a POWER-OFF command is input to the command register (step 1), thememory module initially sets a search address as a start address forsearching the data that has not yet written back to the FLASH from thedata written in the FLASH data copy area of the DRAM (step 2). Uponfinding a flag written to the flag register provided in the datarenewing management circuit CPB corresponding to the search address(step 3), the memory module transfers the DRAM data corresponding to thesearch address to the FLASH (step 4). Completing the transfer, thememory module clears this flag (step 5). The memory module then checkswhether or not the current search address is the final one (step 6). Ifthe current address is not the final address, the memory moduleincrements the current search address (adds one) to set the next searchaddress (step 7) and then repeats the processings in steps 3 to 6. Whenthe current address is the final address, the memory module completesthe processing and shuts off the power supply to the DRAM (step 8).

FIG. 11 shows how the DRAM (e.g., SRAM) operates in the module when datais transferred from the FLASH to the DRAM in response to a LOAD commandinput to the command register. An ACTIVE command A and a row address R,as well as a WRITE command W and a column address C are input fromexternal via the SDRAM interface of the memory module, and a LOADinstruction code Ld is input from external via the I/O signal lines IO0to IO15 (note: the external I/O signal lines IO0 to IO15 are shown inFIG. 1 as I/O signal lines DQ0-DQ15). Thereafter, both start and endaddresses Sa and Ea of the data in the FLASH to be copied into the DRAMare input via the I/O signal line IO0 to IO15. The command register isselected according to the row and column addresses R and C, and the LOADinstruction code Ld, as well as the start and end addresses Sa and Eaare then written in the command register.

The control circuit then reads the data between the start and endaddresses Sa and Ea from the FLASH and holds the data in the buffer. Thecontrol circuit then writes the data in the DRAM1.

The DRAM1 addresses in which data is to be written are translated by thememory management unit MMU so that the start address Sa is translatedinto a row address R0 and a column address C0, and the end address Ea istranslated into a row address R0 and a column address CF for the FLASHcopy area of the DRAM respectively.

Writing data into the DRAM1 is accomplished as follows. Initially, anACTIVE command A is input via the D1-COM line and a row address R0 isinput via the D1-A0 to D1-A15 lines, and then a WRITE command W is inputvia the D1-COM line and a column address C0 is input via the D1-A0 toD1-A15 lines. Thereafter, data is input via the I/O signal lines D1-DQ0to D1-DQ15. The writing of both column address and data is continued upto the final address CF. The writing is terminated by a PRECHARGEcommand P. A high WAIT signal is output between the start and end of thedata writing in the DRAM to denote that data is being transferred to theDRAM.

FIG. 12 shows the operation of the DRAM in the memory module while datais transferred from the DRAM to the FLASH in response to a STORE commandinput to the command register. An ACTIVE command A and a row address R,as well as a WRITE command W and a column address C are input fromexternal via the SDRAM interface of the memory module. Thereafter, aSTORE instruction code St is input via the I/O signal lines IO0 to IO15.Then, both start and end addresses Sa and Ea of the FLASH data to becopied back to the FLASH from DRAM are input via the I/O signal linesIO0 to IO15. The command register is selected according to the row andcolumn addresses R and C, and the STORE instruction code St, and thestart and end addresses Sa and Ea are written to the command register.

The control circuit reads the data from the address range between thestart and end addresses Sa and Ea in the DRAM, and then writes the datain the FLASH. The addresses for reading data from the DRAM1 aretranslated by the memory management unit MMU so that the start addressSa is translated to a row address R0 and a column address C0 and the endaddress Ea is translated to a row address R0 and a column address CF forthe FLASH data copy area in the SDRAM, respectively.

Reading data from the SDRAM1 is accomplished as follows: an ACTIVEcommand A is input via the D1-COM line and a row address R0 is input viathe D1-A0 to D1-A15 lines; and then, a READ command R is input via theD1-COM line and a column address C0 is input via the D1-A0 to D1-A15lines. The reading is continued up to the final column address CF and isterminated by a PRECHARGE command P. A High WAIT signal is outputbetween the start and end of the reading from the DRAM, denoting thatdata is being transferred from the DRAM.

FIG. 13A shows the operation of the DRAM when the work area in the DRAMis accessed, and FIG. 13B shows the operation of the DRAM when the FLASHcopy area in the DRAM is accessed.

The reading operation shown in FIG. 13A will now be described in detail.Initially, an ACTIVE command A and a row address R0 and a READ command Rand a column address C0 are input from external via the SDRAM interface.The control circuit then transfers the ACTIVE command and the rowaddress R0, and then the READ command R and the column address C0, tothe DRAM1. As a result, the target data is output from the I/O signallines D1-DQ0 to D1-DQ15 and is then output to external via the I/Osignal lines IO0 to IO15.

The write operation shown in FIG. 13A is executed as follows. Initially,an ACTIVE command A and a row address R0 and then a WRITE command W anda column address C0 are input from external via the SDRAM interface. Atthis time, target data (In) is also input via the I/O signal lines IO0to IO15. The control circuit then writes the ACTIVE command A and therow address R0, and then the WRITE command W and the column address C0,to the DRAM1. The target data (In) is written to the DRAM via the I/Osignal lines D1-DQ0 to D1-DQ15.

The read operation shown in FIG. 13B is executed as follows. Initially,an ACTIVE command A and a row address RD, followed by a READ command Rand a column address CD, are input from external via the SDRAMinterface. The memory management unit MMU translates the row address RDof the FLASH to a row address RT of the FLASH data copy area and thecolumn address CD of the FLASH to a column address CT of the FLASH datacopy area, respectively. The ACTIVE command A and the row address RT,followed by the READ command R and the column address CT are input tothe DRAM1. The target data is output from the I/O signal lines D1-DQ0 toD1-DQ15 and is then output to external from the I/O signal lines IO0 toIO15.

The write operation shown in FIG. 13B is executed as follows. Initially,an ACTIVE command A and a row address RF, followed by a WRITE command Wand a column address CF, are input from external via the SDRAMinterface. At this time, target data (In) is also input via the I/Osignal lines IO0 to IO15. The memory management unit MMU translates therow address RF of the FLASH to a row address RL of the FLASH data copyarea and the column address CF of the FLASH to a column address CL ofthe FLASH data copy area, respectively. The ACTIVE command A and the rowaddress RL, followed by the WRITE command W and the column address CL,are input to the DRAM1. The target data is output from the I/O signallines D1-DQ0 to D1-DQ15 and is then written in the DRAM.

FIG. 14 shows the operation of the DRAM when a READ command is receivedfrom external while data is read from the DRAM in response to a STOREcommand written in the command register from external. In the case wherean ACTIVE command A and a row address R0 are received from externalwhile the STORE command drives the WAIT signal into High, whereby dataOs is read from the DRAM so as to be transferred to the FLASH, thecontrol circuit issues a PRECHARGE command Ps to the DRAM1 and suspendsthe reading of the data Os that is being transferred from the DRAM tothe FLASH. Thereafter, the control circuit issues an ACTIVE command Aand a row address R0 to the DRAM1. Upon, receiving a READ command R anda column address C0 from external, the control circuit transfers theREAD command R and the column address C0 to the DRAM1 to read data O,which is output from the IO0 to IO15.

Receiving a PRECHARGE command P and a bank address B0 from external, thecontrol circuit transfers the PRECHARGE command P and the bank addressB0 to the DRAM1 to complete the data reading. Thereafter, the controlcircuit issues an ACTIVE command AS, a row address R4, a READ commandRs, a column address C4, a READ command RS, and a column address C8 tothe DRAM1 to restart reading of the data Os to be transferred from theDRAM to the FLASH.

FIG. 15 shows a block diagram of chip 1 (FLASH) according to thisembodiment. Chip 1 is comprised of: a control signal buffer C-BUF; acommand controller CTL; a multiplexer MUX; a data input buffer DI-BUF;an input data controller IDC; a sector address buffer SA-BUF; an Xdecoder X-DEC; a memory cell array MA (FLASH); a Y address counter Y-CT;a Y decoder Y-DEC; a Y gate and sense amplifier circuit Y-GATE/SENS AMP;a data register; and a data output buffer DO-BUF. The operation of chip1 is the same as that of any of the conventional AND FLASH memories. TheAND FLASH memories are often referred to as large capacity flashmemories and classified as NAND flash memories in the broad sense. Inthis specification, the term “NAND flash memory” also denotes an ANDFLASH memory. Chip 1 (FLASH) can be used as a component of the memorymodule in this embodiment.

FIG. 16 illustrates a data read from an AND FLASH memory that maycomprise chip 1. When the chip enable signal F-/CE and the commandenable signal F-CDE are driven into low and the write enable signalF-/WE rises, a READ instruction code Rcode is input via the I/O signallines I/O0 to I/O7. Then, a sector address is input via the I/O signallines I/O0 to I/O7 at the rising of each of the second and third writeenable signals F-/WE.

The 16 kb data corresponding to the input sector address is transferredto the data register from the memory cell array MA. While data istransferred from the memory cell array MA to the data register, theFLASH is busy and the F-RDY/BUSY drives the RDY/BUSY signal into low.When the data transfer ends, data is read from the data registersequentially in units of 8 bits synchronously with the rising of theserial clock signal F-SC and is then output from the I/O signal linesI/00 to I/07.

FIG. 17 shows a block diagram of the memory module in which chip 1 iscomprised of a NAND flash memory. The signals input to the chip 1 are asfollows: the F-/CE is a chip enable signal; the F-/CLE is a commandlatch enable signal; the F-ALE is an address latch enable signal; theF-/WE is a write enable signal; the F-/RE is a read enable signal; theF-/WP is a write protect signal; the F-R/B is a ready/busy signal; andthe I/O0 to I/O7 are I/O signals used to input addresses and data. Inthis way, the memory module can also use a NAND flash memory.

FIG. 18 shows a block diagram of a NAND flash memory used for thismemory module. The NAND flash memory is comprised of: a logic controllerL-CONT; a control circuit CTL; an I/O control circuit I/O-CONT; a statusregister STREG; an address register ADREG; a command register COMREG; aready/busy circuit R/B; a high voltage generator VL-GEN; a row addressbuffer ROW-BUF; a row address decoder ROW-DEC; a column buffer COL-BUF;a column decoder COL-DEC; a data register DATA-REG; a sense amplifierSENSE-AMP; and a memory cell array MA.

The operation of this chip 1 is the same as that of any of theconventional NAND flash memories. As described above, this chip 1(FLASH) can also be used as a component of the memory module in thisembodiment.

FIG. 19 illustrates a data read operation from the NAND flash memoryused as chip 1. When the chip enable signal F-/CE is low, the commandlatch enable signal F-CLE is high, and the write enable signal F-/WErises, a READ instruction code Rcode is input via the I/O signal linesI/O0 to I/O7. Thereafter, the address latch enable signal F-ALE becomeshigh, and the second to fourth write enable signals F-/WE rise. A pageaddress is input via the I/O signal lines I/O0 to I/O7.

The 4 kbit (422-bit) data corresponding to the input page 4 kbit (422bits) address is transferred to the data register DATA-REG from thememory cell array MA. While the data is transferred from the memory cellarray MA to the data register DATA-REG, the FLASH is driven into thebusy state and the F-R/B drives the ready/busy signal to low. When thedata transfer ends, data is read from the data register DATA-REGsequentially in units of 8 bits synchronously with the falling of theread enable signal F-/RE and is output from the I/O signal lines I/O0 toI/O7.

FIG. 20 shows a block diagram of the DRAM in this embodiment. The DRAMis comprised of: an X address buffer X-ADB; a refresh counter REF.COUNTER; an X decoder X-DEC; memory cell arrays MA; a Y address bufferY-ADB; a Y address counter Y-AD COUNTER; Y decoders Y-DEC; a senseamplifier circuit and Y gate (column switch) SENSE AMP. & I/O BUS; aninput data buffer INPUT BUFFER; an output data buffer circuit OUTPUTBUFFER; and a control circuit and timing generator CONTROL LOGIC & TGThe DRAM is preferably a conventional general-purpose SDRAM. In otherwords, the DRAM includes four independent memory banks, and those memorybanks share address input terminals and data I/O terminals, which areused by each of the banks in a time-division manner. This DRAM may beused as a component of the memory module in this embodiment.

As described above, the memory module of the present invention that usesthe SDRAM interface can read data from the FLASH almost at the samespeed as that of the DRAM, since it includes an area reserved in theDRAM that can copy part or all of the data from the FLASH, so that thedata is transferred from the FLASH to the DRAM prior to operation. Whenwriting data to the FLASH, it is also possible to obtain the same writeaccess time as that of the DRAM because data is written to the DRAMonce, and then written back into the FLASH as needed.

When data is read from or written to the FLASH in the memory module,error detection and error correction are performed for the read/writtendata. When the writing fails, a replacement processing is done for thefail address so as to write the data in another address. The processingcan thus be sped up, and the reliability of the memory module isassured.

Because the present invention uses a large capacity DRAM, it is possibleto secure an area that can copy part or all of the data from the FLASHand a large capacity work area, the DRAM can cope with the enhancedfunctions of any cellular phone.

The sizes of the work area and the FLASH copy area to be secured in theDRAM, as well as the management units of those areas can be programmedfrom external and freely selected by the user as appropriate to thesystem.

Second Exemplary Embodiment

FIG. 21 shows a second exemplary embodiment of the memory module of thepresent invention. This memory module is comprised of three chips.Hereinafter, each of the three chips will be described in detail. Chip 1(FLASH) is preferably a non-volatile memory. This non-volatile memorymay be a ROM (Read Only Memory), an EEPROM (Electrically Erasable andProgrammable ROM), a flash memory, or the like. In this exemplaryembodiment, a flash memory is employed. Chip 2 (SRAM+CTL_LOGIC) includesa static random access memory (SRAM) and a control circuit (CTL_LOGIC)that are integrated thereon. The control circuit controls the SRAMintegrated on chip 2 as well as chip 3. Chip 3 is a dynamic randomaccess memory (DRAM). The DRAM is classified into various types such asEDO, SDRAM, DDR, etc. according to the differences in the internalconfigurations and the interface types among them. This memory modulemay be any of those DRAM types, but the SDRAM is employed in thisembodiment as an example.

This memory module receives addresses (A0 to A24) and command signals(S-/CE1, S-CE2, S-/OE, S-/WE, S-/LB, S-/UB, LS-EN, F-EN) input fromexternal. Power is supplied to the memory module via S-VCC, S-VSS,LF-VCC, LF-VSS, LD-VCC, and LD-VSS. Data is input/output to/from thismemory module via the I/O0 to I/O15 lines. So-called SRAM interfaces areused to operate this memory module. It should be noted that some of theabove-mentioned signals may be altered or excluded for purposes ofclarity or convenience in the drawings.

Chip 2 supplies signals required for the operation of chip 1 and chip 3.Chip 2 supplies a serial clock (F-SC), addresses and FLASH data (I/O0 toI/O7), commands (F-CE, F-/OE, F-/WE, F-/RES, F-CDE, F-RDY/BUSY) andpower (F-VCC, F-VSS) to chip 1. Additionally, chip 2 supplies a clock(D1-CLK), addresses (D1-A0 to D1-A14), commands (D1-CKE, D1-/CS,D1-/RAS, D1-/CAS, D1-/WE, D1-DQMU/DQML), DRAM data (D1-DQ0 to D1-DQ15),and power (D1-VCC, D1-VSS, D1-VCCQ, D1-VSSQ) to chip 3.

The command signals input to chip 2 are as follows: the S-/CE1 and theS-CE2 are chip enable signals; the S-/OE is an output enables signal;the S-/WE is a write enable signal; the S-/LB is a lower byte selectsignal; and the S-/UB is an upper byte select signal.

The signals input to chip 1 are as follows: the F-/CE is a chip enablesignal; the F-/OE is an output enable signal; the F-/WE is a writeenable signal; the F-SC is a serial clock signal; the F-/RES is a resetsignal; the F-CDE is a command data enable signal; and the F-RDY/BUSY isa ready/busy signal. The I/O0 to I/O7 are I/O signal lines used to inputaddresses and input/output data.

The chip 2 control circuit (CTL-LOGIC) selects one of the commandregister REG, the SRAM of chip 2, the DRAM of chip 3, and the FLASH ofchip 1 provided therein according to a received address value. Accessesto the command register REG, the SRAM, the DRAM, and the FLASH describedabove can be distinguished according to a value preset in the controlregister provided in the control circuit (CTL_LOGIC). A so-called “SRAMinterface” is preferably used to access each of those areas.

The DRAM is divided into a work area and a FLASH data copy area. Thework area is used as a work memory in which programs are executed, andthe FLASH data copy area is used as a memory to copy data from theFLASH.

To access the SRAM in chip 2, address signals for selecting the SRAM,command signals, and the like are input to the control circuit(CTL_LOGIC). For a read access to the SRAM, data is read from the SRAMand then output to the I/O signal lines (I/O0 to I/O15) of the memorymodule. For a write access to the SRAM, data is input via the data I/Olines (I/O0 to I/O15) of the memory module and then written to the SRAM.

FLASH data can be copied (loaded) into the FLASH data copy area locatedin the DRAM, and the data in the FLASH data copy area in the DRAM can bewritten back (stored) into the FLASH by accessing the command registerREG in the control circuit (CTL_LOGIC) and writing LOAD and STOREinstruction codes therein.

When an address for accessing the command register REG is input to anaddress signal line (A0 to A24), a WRITE command is inputted to acommand signal line (S-/CE1, S-CE2, S-/OE, S-/WE, S-LB, S-/UB), and aLOAD instruction code and both start and end addresses of a FLASH areafor loading are input to the I/O data signal lines (I/O0 to I/O15). TheLOAD instruction code, as well as the start and end addresses forloading are written to the command register. Thereafter, data is readfrom an address range between the start and end addresses for loading inthe FLASH and is transferred to the FLASH data copy area in the DRAM.Consequently, the FLASH data comes to be held in the DRAM.

When a STORE instruction code as well as both start and end addressesfor storing, which are used to select the FLASH, are written to thecommand register, data is written back into an address range between thestart and end addresses for storing in the FLASH from the FLASH datacopy area located in the DRAM.

A value can be preset in the control register provided in the controlcircuit (CTL_LOGIC) so as to determine the address correspondencebetween an address range of the FLASH and an address range of the FLASHdata copy area in the DRAM.

The reliability of the FLASH may be degraded due to repetitive rewritingof data therein, whereby written data is incorrectly read and rewritingis disabled. When data is read from the FLASH, chip 2 (CTL_LOGIC)detects and corrects errors, if any, so as to transfer the correct datato the DRAM.

For example, when data is written in the FLASH, chip 2 (CTL_LOGIC)checks whether or not the data is written correctly. If not writtencorrectly, chip 2 (CTL_LOGIC) writes the data in another address. Thisis a so-called “address replacement processing”. Chip 2 (CTL_LOGIC) alsomanages respective fail addresses, as well as replacement processingsexecuted for those respective addresses.

When the FLASH data copy area in the DRAM is to be accessed, the FLASHarea address range is input via address signal lines (A0 to A24), and acommand is input via a command signal line (S-/CE1, S-CE2, S-/OE, S-/WE,S-/LB, S-/UB). When the command is a READ command, the control circuitof chip 2 accesses the DRAM and reads the target data from the addressrange in the DRAM FLASH data copy area, corresponding to the addressesin the FLASH area. When the command is a WRITE command, write data isinput to the data I/O lines (I/O0 to I/O15) of the memory module andthen input to the DRAM via the DRAM data I/O lines (D1-DQ0 to D1-DQ15).Consequently, both data reading and writing speeds of the FLASH becomeequal to those of the DRAM (in this case, an SDRAM.)

When the work area in the DRAM is to be accessed, address and commandsignals required to access the area are input via the correspondingaddress and command lines. The control circuit (CTL_LOGIC) thengenerates addresses for accessing the work area in the DRAM and accessesthe DRAM. For a read access, data read from the DRAM is output to thedata I/O lines (I/O0 to I/O15) via the DRAM data I/O lines (D1-DQ0 toD1-DQ15). For a write access, write data is input via the data I/O lines(I/O0 to I/O15) of the memory module and input to the DRAM via the DRAMdata I/O lines (D1-DQ0 to D1-DQ15).

The power to chip 3 (DRAM) is supplied from the LD-VCC and the LD-VSSconnected to the D1-VCC, the D1-VSS, the D1-VCCQ, and the D1-VSSQ viathe control circuit (CTL_LOGIC). The power to the FLASH is supplied fromthe LF-VCC and the LF-VSS connected to the F-VCC and the F-VSS via thecontrol circuit (CTL_LOGIC). The command signal PS is used to controlthe power supply to both the DRAM and the FLASH, so that the powersupply is shut off when possible.

When the power supply to the DRAM is shut off, the control circuit(CTL_LOGIC) enables only the data that must be written back into theFLASH to be automatically written back from the DRAM and shuts off thepower supply to the DRAM after the data writing-back is completed. Topower the DRAM again, the DRAM must be initialized. The control circuit(CTL-LOGIC) generates signals required to initialize the DRAM and theFLASH and to control the timings thereof.

To periodically refresh the DRAM, the control circuit (CTL_LOGIC) mayissue the BANK ACTIVE command. Generally, the refreshing characteristicsof the DRAM are degraded at high temperatures. This problem is avoided,however, by providing the control circuit (CTL_LOGIC) with athermometer, whereby the interval for issuing the BANK ACTIVE command athigh temperatures may be narrowed. The DRAM can thus be used in a widertemperature range.

According to the embodiment as described above, it is possible torealize a large capacity memory module, which uses the SRAM interfacemethod and low-price general-purpose SDRAM and FLASH memories. Thememory module preferably has same access speed as that of the SRAM.

The memory module of the present invention can read FLASH data at thesame speed as that of the SRAM because the DRAM includes an area thatcan copy part or all of the FLASH data therein so that the data istransferred to the DRAM from the FLASH prior to access of that data.When data is to be written to the FLASH, it is possible to write data inthe DRAM once and then write the data back into the FLASH only asneeded. Therefore, data can be written back into the FLASH at the samespeed as that of an SRAM.

Because a large capacity SDRAM is used in this example, it is possibleto secure an area that can copy FLASH data, as well as a large capacitywork area in the SDRAM. When data is read from the FLASH, both errordetection and error correction are performed for the read data. Whendata is not written in an address in the FLASH, an address replacementprocessing is accomplished for the fail address. The processing can thusbe done quickly, and the reliability of the memory module is improved.

When the interval for DRAM refreshing executed in the memory module ischanged according to a temperature, the temperature range of the DRAMoperation can be widened, whereby a large capacity memory module with awide operation temperature range can be realized. The present inventionalso preferably provides a memory module that requires a lower dataretention current. In order to address this principle, the interval forrefreshing the DRAM to be executed in the memory module at a lowtemperature is extended, whereby the data retention current is reduced.In order to further reduce the data retention current, the power supplyto the DRAM may be shut off and only the data stored in the SRAM isheld. Consequently, only the minimum data retention current is requiredto hold the necessary data.

FIG. 22 shows a block diagram of chip 2 (SRAM+CTL_LOGIC). Chip 2(SRAM+CTL_LOGIC) is preferably comprised of an SRAM and a controlcircuit (CTL_LOGIC). The SRAM integrated on chip 2 is a conventionalasynchronous SRAM used generally in system design. The control circuit(CTL_LOGIC) is shown as an area enclosed by a broken line in FIG. 22.The control circuit (CTL_LOGIC) occupies most of the space of chip 2except for the SRAM. The control circuit (CTL_LOGIC) is comprised of thecircuit blocks of AS; MMU; ATD; ATD; CTD; R/W BUFFER; CPB; A_CONT; REG;INT; TMP; RC; PM; CLK_GEN; and COM_GEN. Hereinafter, the operation ofeach of those circuit blocks will be described in detail.

The initialization circuit INT initializes both the control register inthe memory management unit MMU and the DRAM when the power is supplied.

The memory management unit MMU translates addresses input from externalaccording to a value preset in the control register and selects thecommand register REG in the register area, the work area in the DRAM,the FLASH data copy area in the DRAM, or the FLASH and provides accessto the selected one. The value in the control register is initialized bythe initialization circuit INT when the memory module is powered. Tochange the value in the control register, a memory management MMU CHANGEcommand may be input to the command register REG When the SRAM isselected, the access switch (AS) sends address and command signals tothe SRAM, whereby the SDRAM is accessed.

The address transition detector circuit (ATD) detects a change in any ofthe address and command signals and outputs pulses. The commandtransition detector circuit (CTD) detects a change in any of the commandsignals and outputs pulses. An access to the memory module begins whenthese detector circuits detect signal changes.

When data is written to an address in the FLASH data copy area in theDRAM, the data renewing address management circuit CPB stores theaddress information.

The command register REG receives and stores commands such as LOAD,STORE, MMU CHANGE, POWER-OFF, as well as start and end addresses forloading, storing, and other functions that are written thereto. The databuffer R/W BUFFER temporarily holds data read/written from/to the DRAMor data read/written from/to the FLASH. The command generator COM_GENgenerates commands required to access the DRAM. The access controllerA_CONT controls all of chip 2 and generates addresses required to accessthe DRAM. The FLASH control signal generator FGEN controlsreading/writing data from/to the FLASH.

The error correction circuit ECC checks whether or not an error isincluded in read data. When an error is included, the circuit ECCcorrects the error. The replacement processing circuit REP checkswhether or not data is written to the FLASH correctly. When data is notwritten to an address correctly, the circuit REP writes the data toanother address previously prepared in the FLASH (address replacementprocessing).

The temperature measuring module (TMP) measures temperatures and outputsa signal according to the measured temperature to both the RC and theA_CONT. The RC is a refresh counter that generates addresses forrefreshing in accordance with the DRAM refreshing interval. Thetemperature measuring module (TMP) outputs a signal that changes therefreshing interval according to the measured temperature.

The power module (PM) controls the power supplies to the control circuit(CTL_LOGIC) of chip 2 and the DRAM. The clock generator (CLK_GEN)generates a clock and supplies the clock to the DRAM and the controlcircuit (CTL_LOGIC).

Next, the operation of this memory module will be described in detail.To access chip 2 (SRAM+CTL_LOGIC), the conventional general asynchronousSRAM method is used to interface the access. When a change occurs in anyof the address signals (A0 to A24) and the command signals (S-/LB,S-/UB, S-/WE, S-/CE1, S-CE2, S-/OE), the ATD detects the change, wherebyan access to the command register REG, the SRAM, the DRAM, or the FLASHbegins.

The value of an address (A0 to A24) input from external is initiallytranslated by the memory management unit MMU. According to thetranslated address, the access target (command register REG, SRAM, DRAM,or FLASH) is determined. The address translation pattern is determinedby a value preset in the control register provided in the memorymanagement unit MMU.

When the command register REG is selected and a LOAD instruction code iswritten to the command register REG, FLASH data is transferred to theDRAM as follows. Initially, the FLASH control signal generator FGENreads data from the FLASH. If the read data contains no errors, the FGENtransfers the data directly to the data buffer R/W BUFFER. If the readdata contains any error, the error correction circuit ECC corrects theerror and transfers the corrected data to the data buffer R/W BUFFER.Thereafter, the DRAM receives a WRITE command from the command generatorCOM_GEN, address signals from the access controller A_CONT, and the datathat was read from the FLASH from the data buffer R/W BUFFER, wherebythe data is written in the FLASH data copy area in the DRAM.

When the command register REG is selected and a STORE command is writtento the command register, data is transferred from the FLASH data copyarea of the DRAM to the FLASH as follows. Initially, the DRAM receives aREAD command from the command generator COM_GEN and address signals fromthe access controller A_CONT, whereby data is read from the DRAM. Thedata read from the DRAM is transferred to the FLASH controller FGEN viathe data buffer R/W BUFFERS and the FLASH control signal generator FGENwrites the data in the FLASH. The address replacement circuit REP checkswhether or not the data is written successfully. If successful, the REPterminates the processing. If not successful, the REP writes the data inanother address prepared beforehand in the FLASH (address replacementprocessing). When such a replacement processing is done, the REP holdsand manages the address information that denotes each address for whichsuch a replacement processing is performed. The data renewing managementcircuit CPB selects the information of each FLASH address in whichwriting has already been sequentially performed and clears the addressinformation. In this way, the data renewing management circuit CPB cankeep management of addresses in which the latest renewed data is held.

When the DRAM work area or the FLASH data copy area are selected and aREAD command is written to the command register, the DRAM receives theREAD command signal from the command generator COM_GEN and addresssignals from the access controller A_CONT, whereby data is read from theDRAM. When the DRAM work area or the FLASH data copy area are selectedand a WRITE command is written to the command register, the DRAMreceives the WRITE command signal from the command generator COM_GEN,address signals from the address controller A_CONT, and data from thedata buffer R/W BUFFER, whereby the data is written in the DRAM.

When the command register REG is selected and a POWER-OFF command iswritten to the command register, the data renewing management circuitCPB transfers the DRAM data corresponding to the address held therein asfollows. Initially, the DRAM receives a READ command from the commandgenerator COM_GEN and address signals from the access controller A_CONT,whereby data is read from the DRAM. The data read from the DRAM istransferred to the FLASH controller FGEN via the data buffer R/W BUFFERand is then written to the FLASH by the FLASH control signal generatorFGEN.

The data renewing management circuit CPB selects the information of eachDRAM address held therein from which data is written in the FLASH andclears the address information sequentially. When all the datacorresponding to the addresses held therein is written to the FLASH, theaddress information in the data renewing management circuit CPB is allcleared.

When the memory module is used at high temperatures, the DRAM refreshinginterval should be reduced so that the refresh process is performed morefrequently. In this memory module, therefore, a temperature measuringmodule TMP measures the temperature and sends the measured temperatureto both the refresh counter and the access controller. When thetemperature rises, the refresh counter decreases the refreshing intervaland outputs a refresh address. When the temperature falls, the refreshcounter can extend the DRAM refreshing interval so as to reduce the dataretention current. When the temperature falls, therefore, the refreshcounter extends the refreshing interval and outputs a refresh address.

An apparatus in which the above memory module is mounted may desirecurrent consumption to be reduced according to the operation state. Adescription will now be made of a method for reducing the powerconsumption of the memory module by changing the operation state withuse of a power module.

Initially, the simplest method for reducing the power consumption asdescribed above is to enable the power module to stop the refresh frombeing performed by the refresh counter with use of the command signalPS. Although the data stored in the DRAM is erased at this time, therefreshing power can be reduced. To further reduce the powerconsumption, the power to the DRAM may be shut off in the memory module.In this case, the power module stops the power supply to the D1-VCC,which is supplied to the DRAM, according to the command signal PS outputfrom the subject apparatus.

To still further reduce the power consumption, the power module may stopthe power supply to a part related to the access to the DRAM on chip 2(SRAM+CTL_LOGIC) according to the command signal PS. In this state, forexample, the power is supplied only to the SRAM, the MMU, and the AS onchip 2 (SRAM+CTL_LOGIC) to enable their operations so that the memorymodule is set in a mode that enables only the accesses to the SRAM. Itmay also be possible to enable the data in the SRAM to be held by thecommand signal PS. In this case, all the power supplies except for theS-VCC and S-VSS supplied to the SRAM may be shut off so that accesses tothe memory module are disabled. In this state, the memory module holdsthe data stored in the SRAM.

To restart the DRAM after the power supply to the DRAM is shut off once,the DRAM must be initialized in addition to restarting of the powersupply to the DRAM. The initialization proceeds normally, but thismemory module uses an initialization circuit INT that instructs theaccess controller A_CONT to use a predetermined initializationprocedure. To restart the DRAM after the DRAM refreshment is stopped,the DRAM must also be initialized. In this case, the initializationcircuit INT instructs the access controller A_CONT to use thepredetermined initialization procedure for the initialization.

FIGS. 23 to 26 show examples of the memory maps in which addresses aretranslated by the memory management unit MMU. The user may select any ofthese memory maps according to a value preset in the control registerprovided in the MMU. Although not specifically limited, it is assumed inthis embodiment that the memory module is provided with a FLASH whosememory capacity is 256+8 Mb, a 2 Mb SRAM, and a 256 Mb DRAM. Adescription will be made hereinafter for typical memory maps used in thememory module.

In the memory maps shown in FIG. 23, the memory management unit MMUtranslates addresses input via the address signal lines A0 to A24 toaddresses used in the command register REG (16 kb), the SRAM dataretention area (2 Mb), the work area (128 Mb) in the DRAM, the FLASHdata copy area (128 Mb) in the DRAM, and the FLASH (256+8 Mb). Althoughnot specifically limited, mapping of the command register REG, the SRAM,the DRAM, and the FLASH begins at the bottom of the address space ineach memory map in this embodiment.

The command register REG holds instruction codes such as LOAD, STORE,and MMU REGISTER CHANGE, as well as the start and end addresses forloading, storing, and the like. The DRAM is divided into a work area(128 Mb) and a FLASH data copy area (128 Mb). The work area is used as awork memory in which programs are executed. The FLASH data copy area isused to copy and hold part of FLASH data.

The data retention area (2 Mb) in the SRAM is localized at the bottom ofthe address space in each memory map. Although this area is duplicatedwithin the DRAM in the memory space, the DRAM is not accessed; only theSRAM is accessed. The SRAM areas can be managed exclusively when thepower supply of the memory module is controlled to hold and use only thedata in the SRAM.

The DRAM area (SHADOW) that is not accessed can be used for redundancy.This memory module is enabled to extend the DRAM refreshing intervalwhen the memory module operates at a low temperature to reduce the powerconsumption. However, when the memory module operates at a lowtemperature, some memory cells (fail bits) might become difficult toretain data. The SHADOW area in the DRAM is used in such a case to holdthe data instead of those fail bits. In FIG. 23, the DRAM includes failbits A and B, and those fail addresses are registered beforehand, sothat the SHADOW area is accessed instead of any of the fail bits towhich an access to the DRAM is attempted. The fail bit is thus saved bythe replacement processing through the use of the SHADOW, whereby therefreshing interval is extended to reduce the power consumption of thememory module when the memory module operates at a low temperature.

To copy part of the FLASH data into the FLASH data copy area, the memorymanagement unit MMU determines the address correspondence between anaddress range in the FLASH data copy area and an address range in theFLASH according to a value preset in the internal register. FIG. 23shows an example of such address correspondence denoting that data inthe A1 (64 Mb) and C1 (64 Mb) areas in the FLASH can be copied into theA (64 Mb) and C area (64 Mb) in the FLASH data copy area of the DRAM,respectively. The address correspondence may be changed so that the datain the B1 (64 Mb) and D1 (64 Mb) in the FLASH can be copied into theFLASH data copy area in the DRAM respectively by changing the valuepreset in the internal control register in the memory management unitMMU.

Although not specifically limited, the FLASH (256+8 Mb) is divided intoa main data area MD-Area (A1, A2, B1, B2, C1, C2, D1, D2: 255.75 Mb) anda replacement area Rep-Area (E1, E2: 8.25 Mb). The main data area isfurther divided into a data area (A1, B1, C1, D1) and a redundant area(A2, B2, C2, D2). The data area is used to store programs, and theredundant area is used to store ECC parity data and other data used todetect and correct errors. Data in the data area in the FLASH istransferred to the FLASH data copy area in the DRAM, or data in theFLASH data copy area in the DRAM is transferred to the data area in theFLASH.

The reliability of the FLASH, when rewriting is repeated therein, isdegraded, whereby written data is incorrectly read and rewriting isdisabled. The replacement area is used in such a case to write data whenthe writing in a fail area (fail area C, fail area D) fails. Althoughthe size of the replacement area is not specifically limited, the sizeshould be determined so as to assure the FLASH reliability.

Next, a process for transferring data from the FLASH to the DRAM will bedescribed. To transfer data from the FLASH A1 data area to the FLASHdata copy area A in the DRAM, a LOAD command as well as start and endaddresses SAD and EAD of the FLASH data area A1 are written to thecommand register. The control circuit (CTL_LOGIC) then reads data fromthe address range denoted by the start and end addresses FSAD and FEADin the FLASH data area A1 and transfers the data to the address rangedenoted by the start and end addresses DSAD and DEAD in the FLASH datacopy area A in the DRAM. The correspondence between those address rangesis determined by the memory management unit MMU.

When reading data from the FLASH, the control circuit (CTL_LOGIC) readsthe data from the FLASH data area A1 and the ECC parity data from theredundant area A2 in the data management unit (8 k bits), and the errorcorrection circuit ECC performs error correction if any error isdetected, whereby only corrected data is transferred to the DRAM.

Data is transferred from the DRAM to the FLASH as follows. To transferdata from the FLASH data copy area A in the DRAM to the FLASH data areaA1, a STORE command as well as start and end addresses SAD and EAD ofthe FLASH data area A1 are written to the command register. The controlcircuit (CTL_LOGIC) then reads the data from the address range betweenthe start and end addresses DSAD and DEAD of the FLASH data copy area Ain the DRAM and writes the data in the address range between start andend addresses FSAD and FEAD of the FLASH data area A1. Thecorrespondence between those address ranges is determined by the memorymanagement unit MMU.

When writing data in the FLASH, the error correction circuit generatesECC parity data in the data management unit (8 kb in this case). TheFLASH control circuit FGEN writes the data read from the DRAM to theFLASH data area A1 and the generated ECC parity data in the redundantarea A2, respectively. The address replacement circuit REP checkswhether or not the writing is done successfully. If successful, the REPterminates the processing. If not successful, the REP selects anotheraddress in the FLASH replacement area and writes the data read from theDRAM in the replacement area E1 and the generated ECC parity data in thereplacement redundant area E2, respectively.

Data is read from the FLASH data copy area A of the DRAM as follows.When an address FAD0 of the FLASH data area A1 and a READ command arereceived from external, the MMU translates the address FAD0 to anaddress DAD0 of the FLASH data copy area A in the corresponding DRAM.Consequently, the DRAM is selected, and FLASH data copied into the DRAMcan be read from the DRAM. In other words, FLASH data can be read at thesame speed as that of the DRAM.

Data is read from the work area in the DRAM as follows. When an addressWAD0 of the work area in the DRAM and a READ command are received fromexternal, the MMU outputs the address WAD0 to the address generatorA_CONT. Consequently, data can be read from the address WAD0 in the DRAMwork area.

Data is written to the FLASH data copy area A in the DRAM as follows.When an address FAD0 of the FLASH data area A1, a WRITE command, andwrite data are received from external, the MMU translates the addressFAD0 to the address DAD0 used in the FLASH data copy area in thecorresponding DRAM. Consequently, the DRAM is selected, and data iswritten to the FLASH data copy area A in the DRAM. Because data iswritten to the FLASH data copy area A in the DRAM corresponding to theFLASH data area A1 in this way, FLASH data can be written to the DRAM atthe same speed as that of the SRAM.

Data is written to the DRAM work area as follows. When an address WAD0of the work area, a WRITE command, and input data are received fromexternal, the address generator A_CONT outputs the address WAD0 to theDRAM. Consequently, data can be written in the address WAD0 in the DRAMwork area.

In the memory map example shown in FIG. 24, the SRAM area is dispersedin a plurality of address spaces. The SRAM address space is thereforeduplicated with the DRAM address space, and access to the duplicatedspace is performed to the SRAM. A plurality of SHADOW areas are used tosave a plurality of fail bits. In this example, the SRAM area is set inunits of 2 kb. This is to adjust to the writing/erasing unit of theFLASH memory. When the same management unit is used for both addressspace and FLASH memory, the OS (operating system) and other programs canmore easily handle memory spaces. When the power supply of the memorymodule is controlled to hold and use only the SRAM data, the SRAM areacan be dispersed in the memory space.

FIG. 25 shows an example of memory maps in which the SRAM and the DRAMare mapped in different address spaces. There is no SHADOW areagenerated due to the duplication in the mapping. Consequently, theaddress space becomes as wide as 258 Mb (DRAM 256 Mb+SRAM 2 Mb).

In the memory maps shown in FIG. 26, the SRAM area shown in FIG. 22 isdivided into 128 areas. As in the example shown in FIG. 25, the addressspace thus becomes wider. Just like the example shown in FIG. 22, whenthe power supply of the memory module is controlled to hold and use onlythe SRAM data, the SRAM area can be dispersed in the memory space. TheMMU can thus allocate the SRAM area and the DRAM area in specifiedaddress spaces. The allocation can be changed easily by changing thevalue preset in the built-in control register of the MMU. Furthermore,to reduce the data retention current, it is only necessary to allocatean address space for storing the target data and to stop the powersupply to the DRAM. This method will realize a memory module thatrequires less data retention current.

FIG. 27A shows a priority order of accesses from external to the DRAM,that is, accesses for refreshing the DRAM and accesses with LOAD andSTORE commands. In FIG. 27, the first priority is given to the accessfor refreshing, the second priority is given to the access fromexternal, and the third priority is given to the access with the LOAD orSTORE command.

FIG. 27B shows the operation of the DRAM, which is accessed with a READcommand (read access) and a REF. command (refreshing access) fromexternal. FIG. 27C shows the operation of the DRAM, which is accessedwith a WRITE command (write access) and a REF. command (refreshingaccess).

When no REF access is performed and an external access (i.e., READ orWRITE) is performed, the external access is accepted by the DRAM andenabled to read/write data therefrom/thereto. When both REF access andan external access are requested, the higher priority REF access isaccepted, and then the external access is accepted. While the refreshingis performed, the WAIT signal is high, which denotes that the DRAM isaccessed.

FIG. 28A shows how data is transferred from the FLASH to the DRAM inresponse to a LOAD command written in the command register. In thiscase, target data is read from the FLASH and then held in the databuffer R/W BUFFER once. Thereafter, the DRAM is accessed to write thedata. The WAIT signal is kept at High until this writing in the DRAM iscompleted. The signal denotes that an access to the DRAM has alreadybegun.

FIG. 28B shows how data is transferred from the DRAM to the FLASH inresponse to a STORE command written in the command register. In thiscase, target data is read from the DRAM and held in the data buffer R/WBUFFER once. Thereafter, the FLASH is accessed to write the datathereto. The WAIT signal is kept at High until the read access to theDRAM is completed. The signal denotes that the DRAM is being accessed.

FIG. 29A shows how the DRAM works in response to a read access fromexternal while a write access is being performed for the DRAM with aLOAD command. Although the type of the external access is notspecifically limited at this time, the access is assumed as a read inthis embodiment. For such an external access, the write access to theDRAM with the LOAD command is stopped once so that the external accesscan be processed. The write access to the DRAM with the LOAD command isrestarted when the external access processing is completed.

FIG. 29B shows how the DRAM works in response to a write/read accessfrom external while a read access is being performed to the DRAM with aSTORE command. Although the type of the external access is notspecifically limited at this time, the access is assumed as a write inthis embodiment. For such an external access, the read access to theDRAM with the STORE command is stopped once so that the external accessmay be processed. The read access to the DRAM with the STORE command isrestarted when the external access processing is completed.

FIG. 30 shows an example of the operation waveform of the memory moduleof the present invention. A0 to A24, S-/CE1, S-CE2, S-/LB, S-/UB, S-/OE,and S-/WE are so-called asynchronous SRAM interface signals to be inputto the memory module. Data I/O signals I/O0 to I/O15 are divided intoinput signals and output signals and represented as DIN and DOUT,respectively. MMU, ATD, and CTD represent output signals from the MMUcircuit, the ATD circuit, and the CTD circuit, respectively. D1-CLK is aclock signal supplied to the DRAM, and D1-COM is a generic name for thecommand signals supplied to the DRAM. D1-A0 to D1-A15 are addresses, andD1-DQ0 to D1-DQ15 are DRAM I/O signals.

Initially, a description will be made for a read access to the DRAM.When address signals are input via the address lines A0 to A24, the MMUcircuit outputs translated addresses. When the ATD circuit detects achange in any of the address lines A0 to A24 and the command lines(S-/CE1, S-CE2, S-/LB, S-/UB, S-/OE, and S-/WE) and addresses andcommands are determined, the ATD outputs pulses. This pulse becomes atrigger for issuing a BANK ACTIVE command A and a row address Ro andthen a READ command R and a column address C0 to the DRAM. The data readfrom the DRAM is output to the D1-DQ0 to D1-DQ15 lines and output to theI/O0 to I/O15 lines via the R/W BUFFER.

An example of a write access will now be described. For a write access,a BANK ACTIVE command A and a row address Ro are issued at the fallingof the ATD signal just like in the above read access. Thereafter, theCTD circuit detects a change in any of the command lines (S-/CE1, S-CE2,S-/LB, S-/UB, S-/OE, and S-/WE) to recognize a write access, and thenoutputs pulses. This pulse becomes a trigger for issuing a WRITE commandW and a column address C0, whereby the write access is processed.

FIG. 31 shows an example of the operation waveform of the memory moduleof the present invention. This waveform denotes that an external readaccess is performed while the DRAM is being refreshed.

To refresh the DRAM, a BANK ACTIVE command A and a row address Ro areissued to the DRAM, and a PRECHARGE command P and a bank address Ba areissued to the DRAM. While this refreshing is performed, the refreshcounter outputs a signal RC that denotes that the DRAM is in a refreshperiod. An external read access, when requested during this refreshingperiod, will be processed as follows. When address signals are input toaddress lines (A0 to A24), the MMU circuit outputs translated addresses.When the ATD circuit detects a change in any of the address lines A0 toA24 and the command lines (S-/CE1, S-CE2, S-/LB, S-/UB, S-/OE, andS-/WE) and addresses and commands are determined, the ATD outputspulses. This pulse triggers a latching of these addresses and commands.When the refreshing ends, a BANK ACTIVE command and a row address Ro,and a READ command R and a column address C0 are issued. The data readfrom the DRAM is output to the D1-DQ0 to D1-DQ15 lines and output to theI/O0 to I/O15 lines via the R/W BUFFER.

FIG. 32 shows a block diagram of an SRAM according to this embodiment.The SRAM is comprised of an X decoder X-DEC; memory cell arrays MA(SRAM); a Y gate Y-GATE; a Y decoder Y-DEC; an input data controlcircuit D_CTL; a control circuit CONTROL LOGIC; and an I/O buffer ofeach signal line. This SRAM is known as “asynchronous” can be employedas a component of the memory module in this embodiment.

According to the embodiments as described above, it is possible torealize a large capacity memory module that uses general-purpose DRAMand SRAM interfaces. In the memory module of the present invention, apart or all of the FLASH data may be copied and transferred to the DRAMfrom the FLASH beforehand, so as to enable FLASH data to be read at thesame speed as that of the DRAM (such as an SDRAM or SRAM). Because thetarget data written in the DRAM once can be written back in the FLASH asneeded, the write access speed also becomes the same as that of theSRAM. When data is to be read from the FLASH, error detection and errorcorrection are performed for the read data, so that a replacementprocessing is accomplished for each fail address in which data is notcorrectly written. Therefore, the processing in the memory module issped up, and the memory module reliability is improved.

Because it is possible to secure a data retention area in the SRAM, aswell as a FLASH data copy area and a work area in the DRAM with use ofthe memory management unit MMU, the memory module of the presentinvention can be used widely for various apparatuses. While the controlcircuit (CTL_LOGIC) of the present invention uses an SRAM as describedabove, the control circuit (CTL_LOGIC) is used to refresh the DRAM. Itis therefore possible to use the DRAM just like an SRAM with noconsideration for refreshing of the DRAM.

Furthermore, when the DRAM refreshing interval is narrowed, the DRAM canalso be used at high temperatures, whereby the temperature range of thememory module can be more widely set. On the other hand, when the DRAMis used at a low temperature, the DRAM refreshing interval is widened,whereby the data retention power consumption can be reduced. The memorymodule can therefore reduce the data retention power consumption.

The power module PM can also be operated to stop the power supply topart or all of the DRAM, thereby limiting the use of the memory area andreducing the data retention power. Furthermore, the power supply to thecontrol circuit can also be stopped to reduce the data retention powerconsumption of the memory module of the present invention.

Third Exemplary Embodiment

FIGS. 33A and 33B show a third exemplary embodiment of the memory moduleof the present invention. FIG. 33A shows a top view and FIG. 33B shows across sectional view through line A-A′ of the memory module,respectively. This memory module enables chip 1 (FLASH) chip 2(CTL_LOGIC), and chip 3 (DRAM) described in the first embodiment or chip1 (FLASH), chip 2 (SRAM+CTL_LOGIC), and chip 3 (DRAM) described in thesecond embodiment to be mounted on a substrate (for example, a printedcircuit board PCB made of glass epoxy) mounted on an apparatus with useof ball grid arrays (BGA). Although not specifically limited, chip 1uses a general-purpose DRAM bear chip at one end of which signal andpower supply pads are disposed in a line, and chip 3 uses ageneral-purpose DRAM bear chip in the center of which signal and powersupply pads are disposed in a line.

The bonding pads on chip 1 are connected to the bonding pads on thesubstrate via bonding wires (PATH2), and the bonding pads on chip 2 areconnected to the bonding pads on the substrate via bonding wires(PATH3). The bonding pads on chip 3 are connected to the bonding pads onchip 2 via bonding wires (PATH1). Chip 1 and chip 2 are connected toeach other via bonding wires (PATH4). The chip-mounted surface of thesubstrate is molded with resin to protect the chips and the wiringsthereon. The surface may further be protected by a metallic, ceramic, orresin cover (COVER).

In this embodiment of the present invention, the memory module can beconfigured with a smaller mounting area because bear chips are mountedon the printed circuit board PCB directly. In addition, because thechips can be disposed close to each other, the wiring among the chipsmay be shortened. Because the bonding wire method is employed for allthe wirings between the chips, as well as between each chip and thesubstrate, the memory module can be fabricated in fewer process steps.Furthermore, because the chips are connected to each other via bondingwires directly, the number of bonding pads and the number of bondingwires on the substrate may be reduced, whereby the memory module can befabricated in fewer process steps.

The memory module may use general-purpose DRAM bear chips that areproduced in large quantities, whereby the memory module can be stablysupplied at a low price. When the substrate surface is protected with aresin cover, the strength of the memory module structure increases. Whenthe substrate surface is protected with a ceramic or metallic cover, thestrength of the memory module structure increases and thecharacteristics of heat flux and shielding are improved.

FIGS. 34A and 34B show a variation of the memory module of the presentinvention shown in FIGS. 33A and 33B. FIG. 34A shows a top view and FIG.34B shows a cross sectional view of the memory module. In this example,ball grid arrays (BGA) are used for mounting and wiring chip 3 (DRAM)and chip 2 (CTL_LOGIC or SRAM+CTL_LOGIC). The bonding pads on chip 1 areconnected to the bonding pads on the substrate via bonding wires(PATH2). This mounting method can omit the bonding between chip 2(CTL_LOGIC or SRAM+CTL_LOGIC) and chip 3 (DRAM), as well as between chip2 (CTL_LOGIC) and the substrate, thereby reducing the number of bondingwires. It is thus possible to reduce the number of fabrication processsteps and further improve the reliability of the memory module.

Fourth Exemplary Embodiment

FIG. 35 shows another embodiment of the memory module of the presentinvention. The memory module in this embodiment is preferably comprisedof four chips. Each of these chips will now be described in detail. Chip1 (FLASH) is a non-volatile memory. The non-volatile memory may be a ROM(Read Only Memory), an EEPROM (Electrically Erasable and ProgrammableROM), a flash memory, or the like. In this embodiment, a flash memory isemployed. Chip 2 (SRAM+CTL_LOGIC) is comprised of a static random accessmemory (SRAM) and a control circuit (CTL_LOGIC) that are integratedthereon. The control circuit controls the SRAM and chips 3 and 4 whichare integrated on chip 2. Chip 3 (DRAM1) and chip 4 (DRAM2) are dynamicrandom access memories (DRAM). DRAMs are classified into various typessuch as EDO, SDRAM, and DDR, according to the differences in theinternal configuration and the interface types among them. Although anytype of DRAM may be used for this memory module, the ADRAM is employedin this embodiment.

This memory module receives addresses (A0 to A24) and command signals(S-/CE1, S-CE2, S-/OE, S-/WE, S-/LB, S-/UB, LS-EN, F-EN) input fromexternal. The power is supplied to this memory module via S-VCC, S-VSS,F-VCC, F-VSS, L-VCC, and L-VSS. The S-I/O0 to S-I/O15 are used toinput/output data. This memory module uses so-called SRAM interfaces foroperations.

Chip 2 supplies signals required for the operation of chips 3 and 4.Chip 2 supplies a serial clock (F-SC), addresses (A0 to A24), FLASH data(I/O0 to I/O7), commands (F-CE, F-/OE, F-/WE, F-SC, F-/RES, F-CDE,F-RDY/BUSY), and DRAM data (D1-DQ0 to D1-DQ15, D2-DQ0 to D2-DQ15) tochip 1. In addition, chip 2 supplies clocks (D1-CLK, D2-CLK), addresses(D1-A0 to D1-A14, D2-A0 to D2-A14), commands (D1-CKE, D2-CKE, D1-/CS,D2-/CS, D1-/RAS, D2-/RAS, D1-/CAS, D2-/CAS, D1-/WE, D2-/WE,D1-DQMU/DQML, D2-DQMU/DQML), DRAM data (D1-DQ0 to D1-DQ15, D2-DQ0 toD2-DQ15), powers (D1-VCC, D2-VCC, D1-VSS, D2-VSS, D1-VSSQ, D2-VCCQ,D1-VSSQ, D2-VSSQ) to chips 3 and 4.

Each of the above commands input to chip 2 will now be described: theS-/CE1 and the S-CE2 are chip enable signals: the S-/OE is an outputenable signal: the S-/WE is a write enable signal: the S-/LB is a lowerbyte select signal: and the S-/UB is an upper byte select signal.

The commands input to chip 1 are as follows: the F-/CE is a chip enablesignal, the F-/OE is an output enable signal, the F-/WE is a writeenable signal, the F-SC is a serial clock signal, the F-/RES is a resetsignal, the F-CDE is a command data enable signal, the F-RDY/BUSY is aready/busy signal, and the I/O0 to I/O7 are I/O signals used to controlthe flash memory respectively.

The control circuit (CTL_LOGIC) of chip 2 selects the command registerof the control circuit (CTL_LOGIC) of chip 2, the SRAM of chip 2, theDRAM of chip 3/chip 4, or the FLASH of chip 1 according to an addressvalue received from external. It is also possible to select the commandregister, the SRAM, the DRAM, or the FLASH according to a value setbeforehand in the control register provided in the control circuit(CTL_LOGIC). The so-called “SRAM interface” is preferably used for theaccess to any of them.

To access an SRAM area in chip 2, the addresses of the SRAM area and thenecessary commands are input to the control circuit (CTL_LOGIC). For aread access, data is read from the SRAM and output via the data I/Olines (S-I/O0 to S-I/O15) of the memory module. For a write access, thewrite data is input via the data I/O lines (S-I/O0 to S-I/O15) of thememory module and written in the SRAM.

When the command register in the control circuit (CTL_LOGIC) is accessedto write a LOAD command or STORE command therein, it is possible to copy(load) FLASH data to the FLASH data copy area in the DRAM or write back(store) the data in the FLASH from the FLASH data copy area of the DRAM.When addresses for accessing the command register are input from theaddress signal lines (A0 to A24), a WRITE command is input from thecommand signal line (S-/CE1, S-CE2, S-/OE, S-/WE, S-/UB), and a LOADinstruction code followed by start and end addresses of a FLASH area areinput from the I/O data signals (I/O0 to I/O15), the LOAD commandfollowed by the start and end addresses are written to the commandregister. Then, the target data is read from the FLASH area between thestart and end addresses, and the data is transferred to the FLASH datacopy areas in DRAM1 and in the DRAM2, respectively. Consequently, theFLASH data is held in the DRAM.

Likewise, when a STORE instruction code followed by start and endaddresses of a FLASH area are written to the command register, thetarget data is written back in the FLASH area between the start and endaddresses from the FLASH data copy area of DRAM1 or DRAM2. The addresscorrespondence between the address range of the FLASH area and theaddress range of the FLASH data copy area in each of DRAM1 and DRAM2 canbe determined by a value preset in the control register provided in thecontrol circuit (CTL_LOGIC).

The reliability of the FLASH, when rewriting is repeated therein, isdegraded, whereby written data is incorrectly read and rewriting isdisabled sometimes. When reading data from the FLASH, chip 2 (CTL_LOGIC)makes error detection and error correction for read data so as totransfer corrected data to the DRAM1/DRAM2. When writing data in theFLASH, chip 2 (CTL_LOGIC) checks whether or not data is writtencorrectly. If not written correctly, chip 2 writes the data in anotheraddress (replacement processing). Chip 2 also manages such a failaddress and the replacement processing performed for such the failaddress.

To access the FLASH data copy area in the DRAM, the addresses of theFLASH area are input from the address signal lines (A0 to A24) alongwith a command signal input from a command line (S-/CE1, S-CE2, S-/OE,S-/WE, S-/LB, S-/UB). When the command signal is a READ command, thecontrol circuit of chip 2 accesses the DRAM to read the target data fromthe address range in the FLASH data copy area of the DRAM correspondingto the address range of the FLASH area via the DRAM data I/O lines(D1-DQ0 to D1-DQ15 or D2-DQ0 to D2-DQ15). When the command signal is aWRITE command, the write data is input from the data I/O lines (S-I/O0to S-I/O15) of the memory module and then input to the DRAM via the DRAMdata I/O lines (D1-DQ0 to D1-DQ15 and D2-DQ0 to D2-DQ15). Consequently,the read and write access times of the FLASH become the same as those ofthe SRAM.

To access the work area in the DRAM, the address and command signalsrequired for the access are input to the command register. The controlcircuit (CTL_LOGIC) then generates the addresses of the work area in theDRAM and accesses the DRAM. For a read access, the data read from theDRAM is output to the data I/O lines (S-I/O0 to S-I/O15) via the DRAMdata I/O lines (D1-DQ0 to D1-DQ15 or D2-DQ0 to D2-DQ15). For a writeaccess, the write data is input from the data I/O lines (S-I/O0 toS-I/O15) of the memory module and input to the DRAM via the DRAM dataI/O lines (D1-DQ0 to D1-DQ15 and D2-DQ0 to D2-DQ15).

The power to DRAM1 is supplied via the LD-VCC and the LD-VSS. LD-VCC andLD-VSS are connected to the D1-VCC, the D1-VSS, the D1-VCCQ, and theD1-VSSQ via the control circuit (CTL_LOGIC). The power supply to theDRAM is controlled by the command signal PS, and the power supply may beshut off as needed. When the power supply to the DRAM is to be shut off,the control circuit (CTL_LOGIC) enables only necessary data to beautomatically written back to the FLASH from the DRAM and then shuts offthe power supply to the DRAM after the writing-back is ended. When thepower supply to the DRAM is to be restored, the DRAM and the FLASH mustbe re-initialized. The control circuit (CTL_LOGIC) generates a signalrequired for the initialization of the DRAM and controls the timing.

The control circuit (CTL_LOGIC) can also issue a BANK ACTIVE commandperiodically to refresh the DRAM. Generally, the refreshingcharacteristics of the DRAM are degraded at high temperatures. To avoidsuch trouble, the control circuit (CTL_LOGIC) may be provided with athermometer so that the interval for issuing the BANK ACTIVE command maybe narrowed at high temperatures, whereby the DRAM may be used in awider temperature range. Furthermore, because two DRAMs are used for thememory module of the present invention, the work area and each FLASHarea are duplicated, so that one data item is held in the two DRAMswhile the refreshing timing is adjusted so that the refreshing is hiddenfrom external, whereby accesses to the memory module are not limited byrefreshing from external.

As described above, according to this embodiment, it is possible torealize a large capacity memory module, which employs the SRAMinterface, has a low-price general-purpose SDRAM and FLASH, and has thesame access speed as that of the SRAM. The memory module of the presentinvention enables the copying of part or all of the FLASH data to besecured in the DRAM so that data is transferred from the FLASH to theDRAM before it is accessed. FLASH data can thus be read at the samespeed as that of the SRAM. When data is to be written to the FLASH, thedata may be written in the DRAM once and then written back into theFLASH as needed. This is why the data write access speed becomes thesame as that of the SRAM.

When data is read from the FLASH, error detection and error correctionare preferably performed for the read data. In the case where data isnot written correctly in an address during writing in the FLASH, thedata is written in another address (address replacement processing),whereby the write processing is sped up and the reliability of thememory module is improved. Because the memory module of the presentinvention uses a large capacity SDRAM, an area that can copy part of orall of the FLASH data and a large capacity work area can be secured inthe SDRAM.

In the memory module of the present invention, which uses a DRAM, theDRAM is refreshed in the module, thereby each DRAM can be used just likean SRAM without consideration to the refreshing of each DRAM duringoperation. In addition, the interval of refreshing performed in themodule may be changed, whereby the temperature range of DRAM operationcan be widened. This is why the present invention can realize a largecapacity memory module with a wider temperature range.

Furthermore, the memory module of the present invention can hiderefreshing of each DRAM from external because data is held in two DRAMsand the refreshing timing of each of the DRAMs is adjusted. Therefore,there is no need to adjust the DRAM refreshing timing to giveconsideration to the refreshing when this memory module is accessed.Consequently, this memory module can be used just like any memory modulethat uses only a conventional SRAM. Therefore, no modification isrequired for any conventional system that uses a large capacity memorymodule.

The present invention also preferably provides a memory module thatrequires less data retention current. The DRAM refreshing in the modulemay be performed at longer intervals especially when operating at a lowtemperature, whereby the data retention current can be reduced. Tofurther reduce the data retention current, the power supply to the DRAMis shut off, and only the data stored in the SRAM is held. Because onlynecessary data is stored in the SRAM and the power supply to the memorythat stores other unnecessary data is shut off in this way, the dataretention current can be minimized to hold the necessary data in thememory module.

FIG. 36 shows a block diagram of chip 2 (SRAM+CTL_LOGIC). Chip 2(SRAM+CTL_LOGIC) is comprised of an SRAM and a control circuit(CTL_LOGIC). The SRAM integrated on chip 2 is a conventionalasynchronous SRAM. The control circuit (CTL_LOGIC) is comprised of: AS;MMU; ATD; CTD; REG; FIFO; CPB; R/W BUFFER; CACHE; A-CONT; INT; TMP; RC;PM; CLK_GEN; FGEN; and COM_GEN located in an area outside the SRAM ofchip 2. This area is enclosed by a broken line in FIG. 36.

Hereunder, the operation of each circuit block of chip 2(SRAM+CTL_LOGIC) will be described in detail. The initialization circuitINT initializes the control register located in the memory managementunit MMU and the DRAM when the power is supplied.

The memory management unit MMU translates addresses received fromexternal and selects the command register REG, the SRAM, the work areain the DRAM, the FLASH data copy area in the DRAM, or the FLASH foraccess according to a value preset in the built-in control register. Thevalue in the control register is initialized by the initializationcircuit INT when the power is supplied. The value in the controlregister is updated in response to an MMU CHANGE command input to thecommand register REG When the SRAM is selected, the access switch (AS)sends address and command signals to the SRAM, whereby the SRAM isaccessed.

Upon detecting a change in any of the address and command signals, theaddress transition detector circuit (ATD) outputs pulses. The commandtransition detector circuit (CTD) also detects a change in any of thecommand signals and then outputs pulses. When those detector circuitsdetect such signal changes, the target memory access begins.

The data buffer R/W BUFFER temporarily holds data before the data isread/written from/to the DRAM. The first-in first-out memory (FIFO) is abuffer circuit that outputs data in the order it is input thereto. TheFIFO temporarily holds data and addresses before the data is written tothose addresses in the DRAM. The cache CACHE temporarily stores dataread/written from/to the DRAM when DRAMs are changed for refreshing andan access is continued for a long time. In addition, the CACHE alsostores data to be written in the DRAM with a LOAD command temporarily.

The data renewing management circuit CPB holds information of addressesor an address range in the FLASH data copy area allocated in the DRAM,in which data is renewed, that is, information of addresses or anaddress range in which data is written.

The command register REG holds instruction codes of commands such asLOAD, STORE, memory management MMU CHANGE, POWER-OFF, as well as startand end addresses for loading, storing, and other functions therein. Thecommand generator COM_GEN generates commands required for accessing theDRAM. The access controller A_CONT controls all of chip 2 and generatesaddresses required for accessing the DRAM. The FLASH control signalgenerator FGEN controls reading/writing data from/to the FLASH.

The error correction circuit ECC checks whether or not any error isincluded in the data read from the FLASH and corrects the error, if any.The replacement processing circuit REP checks whether or not data iscorrectly written in each address in the FLASH. When writing to anaddress fails, the REP writes the data in another address (replacementaddress) prepared beforehand in the FLASH.

The temperature measuring module (TMP) measures the temperature andoutputs a signal corresponding to the measured temperature to the RC andthe A_CONT. The RC is a refresh counter and generates addresses to whichDRAM refreshing is to be performed in accordance with the DRAMrefreshing interval. According to the output signal of the temperaturemeasuring module TMP, the refreshing interval may be changed.

The power module PM controls the power supply to the control circuit(CTL_LOGIC) of chip 2 and the DRAM. The clock generator (CLK_GEN)generates a clock and supplies the clock to the DRAM and the controlcircuit (CTL_LOGIC)

The operation of this memory module will now be described. Access to amemory of chip 2 (SRAM+CTL_LOGIC) is accomplished via a conventionalasynchronous SRAM interface. When the ATD detects a change in any of theaddress signal lines (A0 to A24) and in any of command signal lines(S-/LB, S-/UB, S-/WE, S-/CE1, S-CE2, S-/OE), an access to the commandregister REG, the SRAM, or the DRAM begins. A value input to an addresssignal line (A0 to A24) from external is initially translated by theMMU. Thereafter, an address translation pattern is determined by thevalue preset in a register in the MMU. The translated address determinesthe access destination (command register REG, SRAM, or DRAM).

When the SRAM is selected (to be accessed), the MMU sends the translatedaddress to the SRAM and instructs the access switch AS to transfer acommand. The access to the SRAM begins in response to the commandreceived from the access switch AS. Hereinafter, an access to theasynchronous SRAM is performed.

For a read access to the DRAM, addresses input from external andtranslated by the MMU, as well as commands detected by the ATD, are allsent to the A_CONT. The A_CONT, determining which DRAM is to be accessedaccording to the addresses and the commands received from the MMU,instructs the COM_GEN to issue a command to the DRAM. The A_CONT alsotranslates the addresses received from the MMU to row and columnaddresses of the DRAM and outputs the translated addresses to one of thetwo DRAMs which is to be accessed. The COM_GEN issues a command to theDRAM to be accessed synchronously with the clock generated by theCLK_GEN. Receiving the command and the addresses, the DRAM outputs data,which is then transferred to the I/O0 to I/O15 via the R/W BUFFER. Theread access is thus ended.

For a write access to the DRAM, the A_CONT receives addresses input fromexternal and translated by the MMU, as well as commands and datadetected by the ATD and by the DTD. The A_CONT determines which DRAM isto be accessed according to the received addresses and commands, theninstructs the COM_GEN to issue a command to the DRAM. The A_CONT alsotranslates addresses received from the MMU to addresses of the DRAM andoutputs the translated addresses to the DRAM to be accessed. The COM_GENissues a command to the DRAM to be accessed synchronously with the clockgenerated by the CLK_GEN. The write data is input from the data linesI/O0 to I/O15 and held in the R/W buffer before it is written to theDRAM to be accessed. The write data and the addresses are held in theFIFO once and are then written to the other DRAM after the refreshing isended.

When the memory module is to be used at a high temperature, the DRAMrefreshing interval may be shortened so as to more frequently performthe refreshing. In this memory module, the temperature measuring moduleTMP measures the temperature and sends the measured temperature to boththe refresh counter and the access controller. When the temperaturerises, the refresh counter shortens the refreshing interval and outputsthe addresses for refreshing. On the contrary, when the temperaturefalls, the DRAM refreshing interval may be extended to reduce the dataretention current. The temperature measuring module TMP again measuresthe temperature and sends the measured temperature to both the refreshcounter and the access controller. When the temperature falls, therefresh counter extends the refreshing interval and outputs theaddresses for refreshing.

The user may desire a reduction in the current consumption according tothe operation state of the subject apparatus in which the above memorymodule is mounted. A description will now be made of a method forcontrolling a power supply so as to reduce the power consumption of thememory module according to the operation state of the memory module withuse of a power module.

Initially, the simplest method for reducing power consumption is toenable the power module to stop the refreshing performed by the refreshcounter according to the command signal PS. In this case, the datastored in the DRAM is erased, but the refreshing power will be reduced.To further reduce the power consumption, the power supply to the DRAM isshut off in the memory module. In this case, the power module stops thepower supply to the D1-VCC and the D2-VCC according to the commandsignal PS output from the subject apparatus. Such a shut-off of thepower supply may be performed on both of the DRAMs or may be performedon only one of the DRAMs.

To further reduce the power consumption, the power module may stop thepower supply to a part of chip 2 (SRAM+CTL_LOGIC) which is related tothe access to the DRAM, according to the command signal PS. In thisstate, for example, it is possible that power is supplied only to theSRAM, the MMU, and the AS on chip 2 (SRAM+CTL_LOGIC) so as to put thememory module into a mode in which only the SRAM can be accessed.Furthermore, it is possible to operate the memory module with use of thecommand signal PS so that only SRAM data is held. In this case, all thepower supplies except for the S-VCC and the S-VSS connected to the SRAMare shut off, thereby accesses to the memory module is disabled. In thisstate, the memory module holds data stored in the SRAM.

To restart the DRAM after the power supply thereto is shut off, the DRAMmust be initialized, in addition to restarting the power supply. Whilethe initialization method is a conventional one, the initialization ofthe DRAM in this memory module is accomplished by the access controller(A_CONT) in an initialization procedure instructed by the initializationcircuit (INT).

The DRAM, when it is refreshed, must also be initialized before it isrestarted. The DRAM in this memory module is also initialized by theaccess controller (A_CONT) in an initialization process instructed bythe initialization circuit (INT).

FIG. 37 shows examples of memory maps in which addresses are translatedby the MMU. The user can select any of those memory maps according to avalue preset in the built-in control register of the MMU. Although notspecifically limited, it is assumed in this embodiment that the memorymaps are for a memory module in which the FLASH memory area is 256+8 Mb,the SRAM data retention area is 2 Mb, and the DRAM memory area is 256 Mbin capacity, respectively. In the memory maps shown in FIG. 37, thememory management unit MMU translates addresses input via the addresslines A0 to A24 to those used in the command register REG, the SRAM, thework area in the DRAM, the FLASH data copy area in the DRAM, and theFLASH. One of the REG, the SRAM, the work area, the FLASH data copyarea, and the FLASH is selected and accessed according to the translatedaddresses.

The command register located in the control circuit (CTL_LOGIC) receivesinstruction codes such as LOAD, STORE, MMU register CHANGE, andPOWER-OFF, as well as start and end addresses for loading, storing, andthe like written therein from external. When a LOAD command is writtento the command register REG, the control circuit transfers target datafrom the FLASH to the DRAM. In other words, the control circuit writesthe data to the DRAM. When a STORE command is written to the commandregister, the control circuit transfers target data from the DRAM to theFLASH. In other words, the control circuit reads the data from the DRAM.

The two DRAMs (chips 3 and 4) are preferably mapped to the same addressspace and hold the same data. Each of the DRAMs repeats an access period(working period) and a refreshing period (REF period) that isalternately given priority execution. Each memory access to the DRAMfrom external is performed during a working period.

In this example, the 2 Mb SRAM area is localized at the lower portion ofthe address space. This area is duplicated with the DRAM in the mappingof the memory space, but only the SRAM is accessed in this memory space;the DRAM is not accessed. The SRAM area can be managed to control thepower supply to the memory module so as to hold and use only the data inthe SRAM.

Any DRAM area (SHADOW) that is not accessed can be used to save thememory cells of the DRAM from being lost. While this memory module ispreferably provided with a function that reduces the power consumptionto extend the DRAM refreshing interval when the memory module is used ata low temperature, data retention may be difficult in some memory cells(fail bits). In such a case, this SHADOW DRAM area is used to hold thedata instead of those fail bits. FIG. 37 illustrates a case in which theDRAM includes a fail bit A during a WORK period and a fail bit B duringa REF period. These addresses are registered beforehand, whereby theSHADOW area is used instead of each of those fail bits. In this way, thefail bits are saved by the SHADOW area and the refreshing interval isextended at a low temperature, whereby a memory module with reducedpower consumption may be realized.

FIG. 38 shows the principle of the access controlling method for hidingthe DRAM refreshing from external. The operation of the DRAM of thepresent invention will be understood using a concept in which priorityis given to an access to a bank during a REF period.

FIG. 38A shows an explanatory view of an access priority order. In FIG.38A, DRAM1 is in the WORK period and DRAM2 is in the REF period. FIG.38A also shows DRAM accesses to be performed in response to a refreshrequest, a LOAD command, and a STORE command issued from the CACHE thattakes over an access temporarily, the FIFO that stores write datatemporarily, and the RC.

DRAM1, while it is in the WORK period, is accessed (1) from external. Onthe other hand, DRAM2, while it is in the REF period, gives top priorityto the refreshing (2). Thereafter, data held in the FIFO is written (3)to DRAM2, and data is written back (4) to DRAM2 according to the LOADcommand held in the CACHE. Finally, DRAM2 is accessed (5) according to aLOAD/STORE command. The control circuit (CTL_LOGIC) determines thepriority order among those operations and executes each processing inthe priority order.

The external access (1) is performed, each for 80 ns. However, therefreshing (2), the writing-back from the FIFO (3), the write accessfrom the CACHE (4), and an access by a LOAD/STORE command (5) isexecuted for 70 ns. This memory module makes use of such a timedifference to hide the DRAM refreshing from external.

FIG. 38B shows how read accesses are consecutively accomplished to DRAM1during a WORK period. Only an external access (3) is executed to DRAM1for 80 ns, and the access is completed after the target data is read. Onthe other hand, DRAM2 is refreshed (2) for 70 ns.

FIG. 38C shows how a write access is accomplished to DRAM1. An externalwrite access (1) is initially executed to DRAM1 during a WORK period. Atthe same time, write data is held in the FIFO. In DRAM2 during a REFperiod, top priority is given to the refreshing (2). Thereafter, thedata held in the FIFO is written back (3) in DRAM2. At this time, while80 ns is taken for completing one cycle of operation of DRAM1 during aWORK period, only 70 ns is used for completing one cycle of operation ofDRAM2 during a REF period. Consequently, even while DRAM2 is refreshed,writing in DRAM2 is performed faster than DRAM1. It is thus possible tocatch up with DRAM1 soon after all the data items stored in the FIFO arewritten to DRAM2.

FIG. 39 shows how write and read accesses to/from the DRAM with LOAD andSTORE commands may be hidden from external. FIG. 39A shows how the DRAMis accessed in response to read and write accesses from external while aread access to the DRAM by a STORE command is processed. In FIG. 39A,DRAM1 is in a WORK period and DRAM2 is in a REF period. In DRAM1, onlythe read access (1) from external is executed for 80 ns. On the otherhand, in DRAM2, only the read access (4) to the DRAM with a STOREcommand is processed for 70 ns.

FIG. 39B shows how the DRAM is accessed in response to a write accessfrom external while a write access to the DRAM with a LOAD command isprocessed. In DRAM1, only the write access (1) from external is executedfor 80 ns. At this time, the write data is held in the FIFO. In DRAM2during a REF. period, the write access (5) to the DRAM is processed witha LOAD command. At this time, the write data is held in the CACHE. Afterthis, the data held in the FIFO is written (3) to the DRAM. The dataheld in the CACHE is written back to DRAM1 when DRAM1 goes into a REFperiod. In this case, DRAM2 in a REF period takes 70 ns to end one cycleof operation while DRAM1 in a WORK period takes 80 ns to end one cycleof operation. Consequently, because DRAM2 can write data with a LOADcommand faster than DRAM1, DRAM2 can follow up with DRAM1 soon evenafter writing all the data items are written in the FIFO into the DRAM.

FIG. 39C shows how the DRAM is accessed in response to a write accessfrom external while a write access to the DRAM from the CACHE isprocessed after the DRAM1 is shifted into a REF period and DRAM2 isshifted into a WORK period respectively. In DRAM2, the write access (1)from external is processed for 80 ns and the write data is held in theFIFO. In DRAM1 in a REF period, the write access (4) to the DRAM fromthe CACHE is processed, and the data held in the FIFO is written (3) inthe DRAM. In this case, DRAM1 in a REF period takes 70 ns to end onecycle of operation while DRAM2 in a WORK period takes 80 ns to end onecycle of operation. Consequently, because DRAM1 is faster than DRAM2 inwriting from the CACHE, DRAM1 can follow up with DRAM2 soon even afterwriting all the data items held in the FIFO are written to DRAM1.Internal accesses to the DRAM with LOAD and STORE commands can be hiddenso that external accesses are enabled as described above.

FIG. 40 shows how the two DRAMs work in a time division manner so as tohide DRAM refreshing and internal accesses to the DRAM with LOAD andSTORE commands. FIG. 40A shows an example of DRAM operation at75.degree. C. or under, which is a normal operation temperature range.The two DRAMs (DRAM1 and DRAM2) alternately repeat WORK and REF periods.One of the two DRAMs, which is in a WORK period (displayed as WORK)processes external accesses. Initially, DRAM1 goes into a WORK periodand processes external accesses. On the other hand, DRAM2 is in a REFperiod and gives priority to refreshing. When an external access is awrite, DRAM2 writes data after the refreshing ends.

The memory cells of a DRAM are typically refreshed within 64 ms. In theexample shown in FIG. 40, the WORK period and the REF period are changedat least eight times within this time, so that each of DRAM1 and DRAM2alternately repeats the WORK period and the REF period four times.

A description will now be made for refreshing enabled during a REFperiod and a write access and writing back enabled with a LOAD commandon the presumption that an 8 ms refreshing time, which is one REFperiod, is defined as T1, a time required for writing back data from theFIFO in response to a write access during the T1 is defined as T2, and atime enabled for a write access with a LOAD command is defined as T3.For an SDRAM that is 256 Mb in capacity, the memory cell configurationis 8192 rows.times.512 columns.times.4 16-bit banks. The SDRAM istypically required to be refreshed only 32,768 times (for 8192rows.times.4 banks) for 64 ms. Consequently, in the example shown inFIG. 40A, one DRAM has 4 REF periods for 64 ms, so that the DRAM isrefreshed 8192 times in one REF period (8 ms).

One necessary refreshing time is 70 ns, so that T1 becomes 70uns.times.8192 times=0.574 ms. On the other hand, the maximum number ofexternal write accesses enabled for 80 ms becomes 100,000 times (8 ms/80ns) when all the accesses are write ones. The time T1 required forwriting back data in the DRAM during a REF period is 7 ms (70ns.times.100,000 times). When 4096 write accesses are performed with aLOAD command, the time T3 required for the write accesses with the LOADcommand becomes 70 uns.times.4096 times=0.287 ms.

Consequently, the result of T1+T2+T3 becomes 7.861 ms<8 ms. Thus, itwill be understood that refreshing in a REF period, as well as writeaccesses and writing-back with the LOAD command, can be sufficientlyperformed. In addition, it is also possible to refresh a plurality ofbanks in a REF period in the DRAM simultaneously. In this case, thenumber of refreshing times to be performed in a T1 period may be reducedso that the T1 period can be reduced. When the T1 time is reduced inthis way, it is also possible to reduce the FIFO capacity, as well as toshorten the external access interval so as to speed up the processing ofthe memory module.

FIG. 40B shows a case in which the DRAM refreshing interval is changed.Generally, the DRAM refreshing characteristics are degraded at hightemperatures. Consequently, for example, when the temperature is higherthan about 75.degree. C., the refreshing interval is shortened, wherebydata retention is enabled and the DRAM operation is enabled in a widertemperature range. In this example, the refreshing interval is shortenedto 48 ms when the temperature is high. When the T1 remains the samewhile the T2 is 5.25 ms and the T3 is 0.144 ms, the result of T1+T2+T3becomes 5.97 ms<6 ms. It will thus be understood that refreshing in aREF period, as well as both write access and write-back at the time ofloading can be sufficiently processed.

On the other hand, the DRAM refreshing interval can be shortened whenthe temperature is low to reduce the data retention current. In theillustrated example, the refreshing time is extended to 128 ms, which isdouble, when the temperature is reduced. In this case, the REF periodbecomes 16 ms. When the T1 remains the same, the T2 is 14 ms and the T3is 1.15 ms, with a result T1+T2+T3 of 15.8 ms<16 ms. It will thus beunderstood that refreshing in a REF period, as well as both write accessand writing-back at the time of loading can be sufficiently processed.

While the DRAM operation has been described for each chip in thisembodiment, the operation may be performed for each bank according tothe memory module performance and the memory chip configuration. Inaddition, while the refreshing interval (64 ms) is divided into 8 WORKand REF periods, the refreshing period may be divided into more periodsso as to reduce the FIFO capacity for holding data and addresses. On thecontrary, the refreshing interval may also be divided into fewerdivisions so as to reduce the change-over times between WORK and REFperiods, whereby the control circuit that makes such change-overoperations can be simplified.

FIGS. 41A and 41B show the CACHE operations. FIG. 41A shows a case inwhich a write access is requested from external just before WORK and REFperiods are changed over. In this case, an external access A isperformed when the WORK period of DRAM1 ends. In such a case, the WORKperiod of the DRAM1 is extended by dT until the write access ends. Onthe other hand, DRAM2 goes into a WORK period as scheduled, wherebyDRAM2 stands by without enabling data to be written therein until thewrite access ends. The data that is not written in DRAM2 is held in theCACHE. When an access is performed to an address of the same data asthat held in the CACHE during a WORK period, data is preferablyread/written from/to the CACHE instead of from/to DRAM2. When the accessis a write, data is written as usually to DRAM1 during a REF period viathe FIFO. The data held in the CACHE is written back to DRAM1 in thenext REF period after the WORK period of DRAM2 ends. When thiswriting-back ends, the data in the CACHE is cleared. When the access isa read, the WORK period of DRAM1 is extended only by dT until the accessends.

FIG. 41B shows a case in which an access is performed for longer thanthe WORK/REF period and a case in which the operation cannot becompleted within the extended period dT. The external access B beganwhile DRAM1 is in a WORK period passes the extended period dT, and theaccess is continued in the next REF period undisturbed. In this case,the access is also executed to the CACHE and DRAM1 goes into a REFperiod. DRAM2 goes into a WORK period as scheduled and then into thestand-by state. When the access is a read, data is transferred fromDRAM1 to the CACHE. When the access is a write, the data written in theCACHE is written back into both of DRAM1 and DRAM2 when the access ends.The writing-back is performed when each DRAM goes into a REF period.When the writing-back ends, the data in the CACHE is cleared. In thisway, the CACHE may be used to process accesses to be performed in bothWORK and REF periods, as well as accesses to be performed in one or moreWORK periods.

FIG. 42 shows an example of the operation waveform of the memory moduleof the present invention. A0 to A20, S-/CE1, S-CE2, S-/LB, S-/UB, S-/OE,and S-/WE are signals to be input to the memory module. They areasynchronous SRAM interface signals. Data I/O signals I/O0 to I/O15 aredivided into input signals and output signals and represented as DIN andDOUT. MMU, ATD, and DTD are output signals of the MMU circuit, the ATDcircuit, and the CTD circuit. D1-CLK is a clock supplied to DRAM1 andD1-COM is a nominal name of command signals supplied to DRAM1. DL-A0 toD1-A15 are address signals supplied to DRAM1, and D1-DQ0 to D1-DQ15 areDRAM I/O lines used to input/output data signals of DRAM1.

D2-CLK is a clock supplied to DRAM2 and D2-COM is a nominal name of thecommand signals supplied to DRAM2. D2-A0 to D2-A15 are address signalssupplied to the DRAM (DRAM2). D2-DQ0 to D2-DQ15 are DRAM I/O lines usedto input/output data signals of DRAM2.

A first read access will now be described. When an address is input viaan address line (A0 to A24), the MMU circuit translates the address andoutputs the result. The ATD circuit then detects a change in any of theaddress lines A0 to A24 and the command lines (S-/CE1, S-CE2, S-/LB,S-/UB, S-/OE, and S-/WE) and outputs pulses when both addresses andcommands are determined. This pulse triggers the issuance of a BANKACTIVE command A and a row address Ro and then a READ command R and acolumn address C0 to DRAM1 during a WORK period. The data read fromDRAM1 is output to the D-DQ0 to D-DQ15 and to the I/O0 to I/O15 linesvia the R/W BUFFER. On the other hand, a BANK ACTIVE command A and aPRECHARGE command P are input to the DRAM during a REF period to refreshDRAM2.

A description will now be made for a write access to be processed in thenext cycle. For a write access, a BANK ACTIVE A and a row address Ro areissued to both DRAM1 and DRAM2 at the falling of the ATD signal justlike in the above read access. Because no refreshing is done at the timeof a write access, both commands and addresses are issued to both DRAM1and DRAM2. After this, the CTD circuit detects a change in any of thecommand lines (S-/CE1, S-CE2, S-/LB, S-/UB, S-/OE, and S-/WE) andrecognizes a write operation to be executed, and CTD outputs pulses.This pulse triggers the issuance of a WRITE command W and a columnaddress C0 to both DRAM1 and DRAM2, whereby data is written in thetarget DRAM.

As described above, according to this embodiment, it is possible torealize a large capacity memory module that uses SRAM interfaces andlow-priced DRAMs. The control circuit (CTL_LOGIC) of the presentinvention, which uses DRAMs, refreshes the DRAMs such that each DRAM canbe used just like an SRAM without giving any consideration to therefreshing process. In addition, because two DRAMs are used to hold thesame data and it is possible to adjust the refreshing timing andinternal accesses to each DRAM with LOAD and STORE commands, the DRAMrefreshing and the internal accesses can be hidden from external. Thus,there is no need to give consideration to the DRAM refreshing andinternal accesses to each DRAM so as to adjust timings for accessingthis memory module. Consequently, the memory module may be used justlike any memory module that uses only a conventional SRAM. The largecapacity memory module can be used with any conventional systems withoutmodification. In addition, when the DRAM refreshing interval isnarrowed, it is possible to operate the DRAMs at high temperatures,thereby allowing the memory module to work in a wider temperature range.On the other hand, when the temperature is low, the DRAM refreshinginterval can be extended to reduce the data retention power consumption,whereby the memory module can be realized with reduced data retentionpower consumption.

It is also possible to stop the power supply to part or all of each DRAMwith use of a power module PM to limit the memory area, thereby reducingthe data retention power consumption. In addition, when the power supplyto the control circuit is stopped, the data retention power consumptionof the memory module can further be reduced. In such a case, the dataretention area can be freely specified by the MMU, so that the memorymodule can be used for a wide variety of apparatuses.

Fifth Exemplary Embodiment

FIGS. 43A and 43B show a fifth exemplary embodiment of the memory moduleof the present invention. FIG. 43A shows a top view and FIG. 43B shows across sectional view through line A-A′ of the memory module,respectively. This memory module includes chip 1 (FLASH), chip 2(SRAM+CTL_LOGIC), chip 3 (DRAM1), and chip 4 (DRAM2) that are mounted ona substrate (for example, a printed circuit board PCB composed of aglass epoxy substrate) with use of ball grid arrays (BGA). Although notspecifically limited, chips 3 and 4 are general-purpose DRAM bear chipsin the center of which signal and power supply pads are disposed in aline. Chip 1 is preferably a general-purpose bear chip at one end ofwhich signal and power supply pads are disposed in a line.

The bonding pads on chip 1 are connected to those of the substrate viabonding wires (PATH2), and the bonding pads on chip 2 are connected tothose of the substrate via bonding wires (PATH3). Chips 3 and 4 areconnected to chip 2 via bonding wires (PATH1). Chips 1 and 2 areconnected to each other via bonding wires (PATH4). The top surface ofthe chips, which are mounted on the substrate, is resin-molded toprotect each chip and connection wiring. The top surface of thesubstrate may further be covered by a metallic, ceramic, or resin cover(COVER).

In all of the above embodiments of the present invention, bear chips arepreferably mounted on a printed circuit board PCB directly. It is thuspossible to reduce the chip mounting area of the memory module. Inaddition, because chips can be disposed close to each another on thesubstrate, the wiring between chips may be shortened. Further, becausethe bonding wire method is employed for the wiring between chips and thewiring between each chip and the substrate, the number of process stepsfor fabricating the memory module can be reduced. In addition, becausechips are directly connected to each other via bonding wires, the numberof bonding pads and the number of bonding wires on the substrate can bereduced, whereby the number of process steps for fabricating the memorymodule can also be reduced. Furthermore, because mass producedgeneral-purpose DRAM bear chips are used, the memory module can bestably supplied at a low price. When a resin cover is used, the memorymodule can be configured more strongly. When a ceramic or metallic coveris used, the memory module can be configured more strongly with improvedheat flux and shielding characteristics.

FIGS. 44A and 44B show a variation of the memory module of the presentinvention shown in FIG. 43. FIG. 44A shows a top view and FIG. 44B showsa cross section of the memory module, respectively. In this example,chip 2 (SRAM+CTL_LOGIC) is mounted over both chips 3 and 4. The PATH5 isused for the wiring between chip 2 and chip 3 or 4. The bonding pads onchip 1 are connected to those on the substrate via bonding wires(PATH2), and the bonding pads on chip 2 are connected to those on thesubstrate via the bonding wires (PATH3). Chips 1 and 2 are connected toeach other via the bonding pads (PATH4).

This chip mounting method can reduce the area of the printed circuitboard PCB. In addition, the wiring PATH1 between integrated chips canshorten the wiring, so that the reliability of the wiring can beimproved and the noise radiated externally can be reduced.

Sixth Exemplary Embodiment

FIG. 45 shows an embodiment of a cellular phone that uses the memorymodule of the present invention. The cellular phone is preferablycomprised of: an antenna ANT; a wireless block RF; a base band block BB;a voice codec block SP; a speaker SK; a microphone MK; a processor CPU;a liquid crystal display LCD; a keyboard KEY, and the memory module MEMof the present invention.

The operation of the cellular phone will now be described. A voicereceived via the antenna ANT is amplified in the wireless block andinput to the base band block BB. The base band block BB converts theanalog signals of the voice to digital signals, and an error correctionis performed for the signals. These signals are then decoded and outputto the voice codec block SP. When the voice codec block SP converts thedigital signals to analog signals and outputs them to the speaker SK,the voice on the other side of the connection is output from the speakerSK.

A description will now be made for a series of operations for accessinga home page on the Internet to down-load music data, play back themusic, and save the down-loaded music data from a cellular phone. Thememory module MEM stores a basic program and application programs (mail,Web browser, music play-back, and game programs). When the user startsup the Web browser from the keyboard KEY, the Web browser program storedin the FLASH provided in the memory module MEM is transferred to theDRAM located in the same memory module. After this program transfer, theprocessor CPU executes the Web browser program in the DRAM, and the Webbrowser is displayed on the liquid crystal display LCD. When the useraccesses a desired home page and specifies down-loading of desired musicdata from the keyboard, the music data is received via the antenna ANT,amplified in the wireless block RF, and input to the base band block BB.The base band block BB converts the analog signals of the music data todigital signals. Thereafter, both error correction and decoding areperformed on the signals. Finally, the music data consisting of digitalsignals is saved in the DRAM in the memory module MEM and thentransferred to the FLASH.

The user then starts the music playback program using the keyboard KEY.Then, the music playback program is transferred from the FLASH in thememory module MEM to the DRAM located in the same memory module. Whenthe program transfer to the DRAM completes, the processor CPU executesthe music playback program in the DRAM and the program is displayed onthe LCD. Thereafter, the user specifies listening to the musicdown-loaded to the DRAM from the keyboard. The processor CPU executesthe program to process the music data held in the DRAM, whereby the usercan listen to the music output from the speaker SK.

At this time, the large capacity memory module of the present inventionholds both Web browser and music playback program in the DRAM, and theprocessor CPU executes both of the programs simultaneously. In addition,the CPU may start up the e-mail program to send/receive e-mailsconcurrently. The Web browser is preferably held in the DRAM in thememory module MEM even when idle. The Web browser can thus be restartedimmediately. When the user inputs a command for shutting off the powersupply, the memory module operates only the SRAM and holds the minimumdata to minimize the power consumption.

As described above, the use of the memory module of the presentinvention enables many mails, application programs, music data, stillimage data, motion picture data, and the like to be stored, as well aslots of music and a plurality of programs to be played back and to beexecuted, respectively.

Nothing in the above description is meant to limit the present inventionto any specific materials, geometry, or orientation of parts. Manypart/orientation substitutions are contemplated within the scope of thepresent invention. The embodiments described herein were presented byway of example only and should not be used to limit the scope of theinvention.

Although the invention has been described in terms of particularembodiments in an application, one of ordinary skill in the art, inlight of the teachings herein, can generate additional embodiments andmodifications without departing from the spirit of, or exceeding thescope of, the claimed invention. Accordingly, it is understood that thedrawings and the descriptions herein are proffered by way of exampleonly to facilitate comprehension of the invention and should not beconstrued to limit the scope thereof.

1. A memory module mounted in a package, comprising: a non-volatilememory; a random access memory; a controller controlling thenon-volatile memory and the random access memory; a controllercontrolling the non-volatile memory and the random access memory; acommand register written an instruction code; a plurality of externalcommand signal terminals; a plurality of external address terminals; anda plurality of external data terminals, wherein the controller reads outdata from the non-volatile memory and writes the data read out from thenon-volatile memory to the random access memory when a load instructioncode is written into the command register, wherein when command signalsinputted to the plurality of command signal terminals indicate a writeoperation and address signal inputted to the plurality of externaladdress terminals indicate an access to the command register, the loadinstruction code is written into the command register via the pluralityof external data terminals, and when command signals inputted theplurality of command signal terminals indicate the write operation andaddress signal inputted to the plurality of external address terminalsindicates an access to the random access memory, data inputted to theplurality of external data terminals is written into the random accessmemory.